The origin of the name "Grand Slams"
from the US Open site
The term 'Grand Slam' originated from Don Budge's achievement of winning the French Open, Wimbledon, the US Open and the Australian Open in 1938. The distinguished American writer Allison Danzig suggested that like a successful bridge player, Budge had scored a 'Grand Slam' of victories in the four major tennis events in one calendar year.
I didn't know it comes from bridge