Rarely" and "seldom" are synonymous and interchangeable. Example: I seldom/rarely go to the movies/races

i rarely get online(you don't have time so you rarely get online) i seldom drink wine( you don't like wine so you seldom drink wine) when you don't do something often or sometimes or most of the time. we call them adverb of frequency!

Rarely and seldom both indicate low frequency. They can be used in the same contex I rarely go to the beach I seldomly do anything useful Another word for these two is 'hardly ever' If you want to find a word which indicates even low frequency than the above mentioned use hardly or barely ...

"rarely" has lower frequence than "seldom".It's the best diffiences.