I've read Manning's Big Data Lambda Architecture (http://www.manning.com/marz/BD_meap_ch01.pdf) and still not able to get why it's named 'Lambda'. Is it kinda code-name or name of system this architecture is based on?
It was chosen by the American mathematician Alonzo Church, who needed a Greek letter to denote the operator for functional abstraction when he was developing the theory of computation in the 1930s. Different people asked him why he chose that particular letter, and he gave them different answers (but the bottom line is, he didn't really care very much). For a little more detail and some links, see http://www.lambdafaq.org/why-are-lambda-expressions-so-called/