Babe in arms

A babe in arms is a very young child, or a person who is very young to be holding a position.

Babe in the woods

A babe in the woods is a naive, defenceless, young person.

Baby boomer

(USA) A baby boomer is someone born in the years after the end of the Second World War, a period when the population was growing very fast.

Back burner

If an issue is on the back burner, it is being given low priority.

Back foot

(UK) If you are on your back foot, you are at a disadvantage and forced to be defensive of your position.

Back number

Something that's a back number is dated or out of fashion.

Back the wrong horse

If you back the wrong horse, you give your support to the losing side in something.

Back to back

If things happen back to back, they are directly one after another.

Back to square one

If you are back to square one, you have to start from the beginning again.

Back to the drawing board

If you have to go back to the drawing board, you have to go back to the beginning and start something again.

Back to the salt mines

If someone says they have to go back to the salt mines, they have to return, possibly unwillingly, to work.

Back to the wall

If you have your back to the wall, you are in a difficult situation with very little room for manoeuvre.

Backseat driver

A backseat driver is an annoying person who is fond of giving advice to the person performing a task or doing something, especially when the advice is either wrong or unwelcome.

Bad Apple

A person who is bad and makes other bad is a bad apple.

Bad blood

If people feel hate because of things that happened in the past, there is bad blood between them.

Bad egg

A person who cannot be trusted is a bad egg. Good egg is the opposite.

Bad hair day

If you're having a bad hair day, things are not going the way you would like or had planned.

Bad mouth

(UK) When you are bad mouthing,you are saying negative things about someone or something.('Bad-mouth' and 'badmouth' are also used.)

Bad shape

If something's in bad shape, it's in bad condition. If a person's in bad shape, they are unfit or unhealthy.

Bad taste in your mouth

If something leaves you with a bad taste in your mouth, you feel there is something wrong or bad about it.

Bad workers always blame their tools

"A bad worker always blames their tools" - If somebody does a job badly or loses in a game and claims that they were let down by their equipment, you can use this to imply that this was not the case.

Bag and baggage

Bag and baggage means all your possessions, especially if you are moving them or leaving a place.

Bag of bones

If someone is a bag of bones, they are very underweight.

Bag of nerves

If someone is a bag of nerves, they are very worried or nervous.

Baker's dozen

A Baker's dozen is 13 rather than 12.

Bald as a coot

A person who is completely bald is as bald as a coot.

Ball is in your court

If the ball is in your court, it is up to you to make the next decision or step.

Balloon goes up

When the balloon goes up, a situation turns unpleasant or serious.

Ballpark figure

A ballpark figure is a rough or approximate number (guesstimate) to give a general idea of something, like a rough estimate for a cost, etc.

Balls to the walls

(USA) If you do something balls to the wall, you apply full acceleration or exertion.

Banana republic

Banana republic is a term used for small countries that are dependent on a single crop or resource and governed badly by a corrupt elite.

Banana skin

(UK) A banana skin is something that is an embarrassment or causes problems.

Bandit territory

An area or an industry, profession, etc, where rules and laws are ignored or flouted is bandit territory.

Baptism of fire

A baptism of fire was a soldier's first experience of shooting. Any unpleasant experience undergone, usually where it is also a learning experience, is a baptism of fire.

Bar fly

A bar fly is a person who spends a lot of time drinking in different bars and pubs.

Bare your heart

If you bare your heart to someone, you tell them your personal and private feelings. ('Bare your soul' is an alternative form of the idiom.)

Barefaced liar

A barefaced liar is one who displays no shame about lying even if they are exposed.

Bark is worse than their bite

Someone who's bark is worse than their bite may well get angry and shout, but doesn't take action.

Barking up the wrong tree

If you are barking up the wrong tree, it means that you have completely misunderstood something or are totally wrong.

Barkus is willing

This idiom means that someone is willing to get married.

Barrack-room lawyer

(UK) A barrack-room lawyer is a person who gives opinions on things they are not qualified to speak about.

Barrel of laughs

If someone's a barrel of laughs, they are always joking and you find them funny.

Basket case

If something is a basket case, it is so bad that it cannot be helped.

Bat an eyelid

If someone doesn't bat an eyelid, they don't react or show any emotion when surprised, shocked, etc.

Bated breath

If someone says they're waiting with bated breath, they're very excited and find it difficult to be patient.('Baited breath' is a common mistake.)

Bats in the belfry

Someone with bats in the belfry is crazy or eccentric.

Batten down the hatches

If you batten down the hatches, you prepare for the worst that could happen to you.

Batting a thousand

(USA) (from baseball) It means to do something perfectly.

Battle of nerves

A battle of nerves is a situation where neither side in a conflict or dispute is willing to back down and is waiting for the other side to weaken. ('A war of nerves' is an alternative form.)

Be all ears

If you are all ears, you are very eager to hear what someone has to say

Be careful what you wish for

If you get things that you desire, there may be unforeseen and unpleasant consequences.('Be careful what you wish for, lest it come true.' and 'Be careful what you wish for; you may receive it.' are also used.)

Be on the pig's back

If you're on the pig's back, you're happy / content / in fine form.

Be out in force

If people are out in force, they are present somewhere in large numbers.

Be out in left field

(USA) To be out in left field is not to know what's going on. Taken from baseball, when youngsters assign less capable players to the outfield where the ball is less likely to be hit by a young player. In business, one might say, 'Don't ask the new manager; he's out in left field and doesn't know any answers yet.'

Be that as it may

Be that as it may is an expression which means that, while you are prepared to accept that there is some truth in what the other person has just said, it's not going to change your opinions in any significant manner.