Assuming that by lambda you mean "an anonymous function"[1], for most intents and purposes they are, except their returns are non-local whereas functions usually have local returns.

However blocks are special forms of the language, unless reified to procs they can only be passed as parameter (not returned), and a method can only take one block. They also have some oddities in how they interact with parameters (unless reified to lambda procs).

[1] because Ruby has something called "lambda procs"