A hard enquiry, or credit application enquiry, is recorded on your credit file when you actually apply for credit: a loan, a card, a limit increase, sometimes a power or phone account. It is visible to other credit providers and feeds into credit scoring.
One hard enquiry is unremarkable; it is the normal record of borrowing happening. The damage comes from clusters: several applications in a short window read to scoring models like a borrower under pressure, and can drag a score at exactly the moment it is being judged.
The practical rules are simple. Apply rarely and deliberately. Shop for pricing with quote enquiries, not applications. And let the hard enquiry happen once, at the end, when you have chosen an offer and asked the lender to proceed, which is how the sequence works at BorrowClub.
Checking your own credit file is neither kind of enquiry and never affects your score.