Ska punk is a fusion music genre that combines ska and punk rock. It achieved its highest level of commercial success in the United States in the late 1990s. Ska-core (sometimes spelled skacore) is a subgenre of ska punk, blending ska with hardcore punk.
The characteristics of ska punk vary, due to the fusion of contrasting genres. The more punk-influenced style often features faster tempos, guitar distortion, onbeat punk rock-style interludes (usually the chorus), and punk-style vocals. The more ska-influenced style of ska punk features a more developed instrumentation and a cleaner vocal and musical sound. The common instrumentation includes electric guitar, bass guitar, drums, brass instruments (such as trombones or trumpets), saxophones, and sometimes an organ. (Source)
The genre was given birth by 80's ska-punk band Operation Ivy. Many bands were influenced by Operation Ivy and began paying the genre with their own twist. The more popular early Ska-Punk bands consisted of Less Than Jake, Rancid, The Mighty Mighty Bosstones, and Goldfinger. .