[Mythtv-translators] How to translate "preroll + head start"?

[ikke]

grep "Waiting to pass preroll + head start" -A2
mythtv-trunk/mythtv/i18n/mythfrontend_*.ts

Gives results people have translated it... But what the heck does it
even mean in english? Preroll is likely the "what happened in previous
episode" stuff, but what is head start?

And is there a way to identify that in MythTV? This is something new,
but I don't get exactly what it means, please try to explain if you
do.