A lot of posts tag cuckoldry or infidelity with both tags despite them being different
I, as a person who enjoys cuck, but NTR and cheeting makes my skin crawl, have been doing my best to edit posts so they only have the correct tags
The wikis for each tag describes them more specifically, but in summery
If the person consents and gains pleasure from their partner having sex with someone else then it's cuckold
If they don't consent to their partner doing so, it's cheating and should be tagged infidelity
If the person consents but is not gaining pleasure than it is an open relationship/polyamory but shouldn't be tagged as either