What is a Translation Lookaside Buffer?
It is an associative cache that stores the physical addresses of the recently accessed virtual memory pages. It allows to bypass the translation mechanism quite often.
Given a virtual address we are first trying to find the address of its virtual page in TLB. If we succeed, we use it and just add an offset from its start. Otherwise we have to crawl through all levels of page tables to perform the full address translation. The latter will add a new entry into TLB and the subsequent accesses will be faster.