Answer 1

Lambdas are essentially disposable functions.

It varies depending on the language. Python uses lambda <input variable(s)> : <expression(s)> and returns the output of the expression with the variable(s) passed in.

e.g. lambda x: x**2 will return x squared for an input variable x.

Also, if assigned to an operator they can be called as a normal function, e.g.:
>>> a = lambda x:x**2
>>> a(3)
9

Answer 2

in which language?