Coder refers to someone who engages in the act of writing source code and has a very casual, possibly even negative connotation.
A programmer refers to someone who writes software, which has a neutral connotation.
Developer or dev refers to someone who develops software, which may or may not involve writing it, but probably does.
Software engineer and computer scientist are more formal terms for those with degrees or other professional qualifications.
SE is a commonly used abbreviation in speech for a software engineer, but CS is only used for computer science itself, not the people who practice it.