Lead instrument is the name given to someone who is the most advanced player of their instrument in their ensemble. This is also referred to as the first chair, principal, first position, or first [name of instrument].
In addition, monosynth synthesizer patches are often called leads, for their frequent use on melody parts in dance and electronic music. These patches are often legato, meaning filters and modulation are continued across a series of held notes, and portamento can be used to create a pitch bend transition up or down to other notes.
In the music sequencing computer program Reason, there is a folder in the default sound bank of monosynth lead patches, polysynth patches, and bass synthesizer patches.