There's no name space in Emacs lisp, so people use various prefixes to avoid name clash. Section D.1 of Emacs lisp reference manual recommends using a short prefix followed by one or two hyphen(s):
• You should choose a short word to distinguish your program from other Lisp programs. The names of all global symbols in your program, that is the names of variables, constants, and functions, should begin with that chosen prefix. Separate the prefix from the rest of the name with a hyphen, ‘-’. This practice helps avoid name conflicts, since all global variables in Emacs Lisp share the same name space, and all functions share another name space(1). Use two hyphens to separate prefix and name if the symbol is not meant to be used by other packages.
See this questionthis question about why elisp does not have namespaces.