The eephus pitch---also known as the blooper, the folly floater, LaLob and a few other designations---is a very slow, high-arcing curveball that can rise as much as 20 feet in the air before descending. It is thrown straight overhand, and it came about of necessity. Decades ago Rip Sewell sustained an injury that required him to alter his pitching delivery, and he came up with this one. It can be very effective---or it can be the ultimate in gopher balls, depending on who's batting; Ted Williams once got a homer off that pitch. There are some pitchers using it nowadays, but by and large it is very much a trick pitch and not at all widespread.
Interestingly, the word "eephus" also had another meaning. Lefty Gomez would often tell a pitcher to "give it the old eephus" when he wanted that pitcher to put something extra on the ball. 8) :baseballpitcher: