From The Collaborative International Dictionary of English v.0.48 :
lead-in \lead-in\ n.
1. (Elec.) a wire connecting an antenna to a receiver or a
transmitter to a transmission line.
[WordNet 1.5]
2. (Radio and Television Broadcasting) The short segment of a
program or program script introducing and immediately
preceding another part of the program or a commercial.
[PJC]
From WordNet (r) 3.0 (2006) :
lead-in
n 1: the introductory section of a story; "it was an amusing
lead-in to a very serious matter" [syn: lead, lead-in,
lede]
2: wire connecting an antenna to a receiver or a transmitter to
a transmission line