Selfshipping (or yumeshipping) is the act of shipping oneself with a fictional character! It can be any character from any media, or even one that you created yourself! It's all mainly for fun, although some people may use it as a coping mechanism or feel genuine romantic/sexual attraction towards their F/O (fictional other).

People who have F/Os are aware that their F/Os are not real, but may create scenarios or design interactions between them as if they were real! Everyone has different ways of expressing love for their F/O whether it be platonic, romantic, familial, or any other relationship type!
Many selfshippers may create fanfiction with their F/O with them as a self-insert character, create fanart, or create headcanons between them and their F/O. There are many different ways selfshippers can express love towards their F/O, and these are only just a few examples!
Selfshippers can also be referred to as "yumejoshis", meaning "dreaming girl" in Japanese.