No difference. edict means entity dictionary, it contains data about entities that are networked to the client.
"s" means structure so "entity dictionary structure". This struct is defined here:
https://github.com/alliedmodders/hls...ne/edict.h#L19 (think of it like "enum" in pawn).
"t" in edict_t comes from "type". edict_t is an "alias" of "struct edict_s".
https://github.com/dreamstalker/rehl...n/const.h#L786
In C, when you declare a structure and want to use it as a data type, you have to specify "struct struct_name" everywhere, which gets annoying. It is a common practice to define a type like "edict_t" which is a synonym of "struct edict_s". It is cleaner and shorter.
tl;dr
Code:
struct edict_s* my_var;
edict_t *my_other_var;
these are equivalent