Llanfairpwllgwynllgogerychwyrndrobwllllantysiliogogogoch is a village on the island of Anglesey. What does it mean?

As you say, this is a village on the Welsh island of
Anglesey.  The name is mostly a made up one.  Thie village did not originally have such
a long name.  Instead, much of the name was made up so that the village would have a
very long name and could gain publicity through having that
name.

The name itself is said to mean "St Mary's Church in
a hollow of white hazel near the swirling whirlpool of the church of St. Tysilio with a
red cave."

The name was not totally made up.  The village
already had a pretty long name, which was--and still is--Llanfair Pwllgwyngyll.   That
part of the name meant "St Mary's church in the hollow of the white
hazel."