Isolation exercises are movement that target a specific area by using one muscle group or joint. Isolation movements are best used once you have built a good base level of strength by doing compound exercises. However, they are also used if you are recovering from an injury and need to focus a particular joint or muscle. By targeting one area, you can focus on strengthening that area and avoid fatiguing other areas.
Examples of isolation movements include: bicep curl, hamstring curl, leg extensions, calf raises, tricep extensions, reverse pec deck fly.