new to technical termsI. Whats 51/base mean?

[Android Central Question]

Hi.. I am very new to technical terms but very interested in it also.. I am in the middle of making room on my sony xperia (android opp oreo) and i have come across this list of cache to clear bit am not entirely sure what it means.. 'path/storage/51/base' thas not Exactly how its typed but is it something to do with a rom that was updated or the android os? as its a list of around 20and all on the same date? Thanks