In tennis, the term Qualifier can refer to one of two things. It can mean a term used to refer to the qualifying rounds of a tennis tournament. Players who are not seeded will have to go through the qualifiers in order to get their spots.
On the other hand, Qualifier can also refer to a player who made it through the qualifying rounds and into the main matches.
In Grand Slams, 128 players compete in the qualifying tournament for 16 spots in the main draw. To make it through, a player must win three rounds of matches.
Emma Raducanu is famous for being a US Open qualifier who ended up winning the women’s singles category.
Here is an example of a qualifying match from the 2022 Australian Open:
Zizou Bergs vs Radu Albot - Australian Open 2022 Qualifying 1st Round Highlights – [Qualifier][1]
[1]: https://www.youtube.com/watch?v=4Ik9xFhAYz4