Trim, Cut, Split, and Splice are all done by 
cutting your video clips.
When you trim your video, you remove the head and/or the tail of the clip (much like giving your hair a trim: you’re sprucing it up, but not touching the ‘meat’).
A cut is mostly referred to when you remove a section of your video clip, so you cut in two places and lift out the middle section and join the leftover video back together. If you have a very long video, you might just cut it into sections to work with separately, then you’re splitting your video. When you join two video clips together, you splice them.
In all cases make sure you SAVE AS your entire video clip before you edit away. Depending on your software, you might lose your cut or trimmed part of the clip (this goes especially for in-phone apps!).