Words are defined by consensus and use. To a lot of people "functional" means having first-class functions (in particular: functions can be defined anywhere (i.e. the language has closures) and functions are first-class values (i.e. functions can be passed as function parameters and returned from functions; function values can be expressed separately from assignment (i.e. the language has lambdas))) and programming in a style that makes use of map, reduce, and filter; more generally programming with immutable values and functions that return transformations of those values (as distinct from programming with pervasive state that is mutated). This is by no means the only way to write Python, but it's practical in Python to a much greater extent than it is in, say, Java.
