If you are not familiar with painters tape, it is tape created for the purpose of covering a surface next to the surface are you painting. Therefore any drippage or mis-strokes will paint the tape and not the surface you don’t want painted.
One of the good things about painters tape is that it only adheres lightly to the surface. This way you can remove it from the wall without causing any damage. In this sense it is similar to post it notes.
Due to its light adherence painters tape has a lot of other uses besides painting. You can use the tape for taping up pictures, kids artwork or other such items which would normally get destroyed if you used scotch tape. You can also use painters tape to create removable labels.
Note that if you are going to use painters tape for actual painting the best painting tape I have found is Frog Tape. You can find in on Amazon at the following link: Frog Tape 1396748 Multi-Surface Painting Tape.94 Inches Wide x 45 Yards Long, Green