stateless. A stateless server is one which treats each request as an independent transaction, unrelated to any previous request. This simplifies the server design because it does not need to allocate storage to deal with conversations in progress or worry about freeing it if a client dies in mid-transaction.
An expression in a programming language is a combination of one or more explicit values, constants, variables, operators, and functions that the programming language interprets (according to its particular rules of precedence and of association) and computes to produce (to return, in a stateful environment) another value.
Lambda expressions are compact function-like blocks of code that serve as predicates, initializers, and in event-driven apps. Lambdas rid you of the tedium of writing boilerplate code; you only have to code the actual functionality.