What's the difference between a spleen rupture and a spleen laceration?

Rupture more severe: A splenic laceration means a single cut on the spleen which if not deep may not require surgery. A splenic rupture often signifies more severe injury and a higher likelihood of requiring surgery.

Different extent: They are all part of the continuum of splenic injury. A laceration is an injury to just part of the spleen, rupture is a more extensive injury. Most splenic injuries these days are managed without an operation. However if there is significant bleeding from it, it may require removal or repair of the spleen.