To lead a climb with no falls or dogging and with no previous attempts on the climb. Two variations exist: the onsight flash (where the climber has never seen the climb before) and the beta flash (where the climber has studied the climb before or has seen someone do the climb). See there.
To climb a route first time, with out fall. Beta may have been acquired before the ascent.
On-sight with beta.
Climb a route without falling.
To lead a climb, placing one's own protection, without falling on one's first attempt on the route. Beta okay. As distinguished from redpoint and on-sight.
A red point ascent (first try on lead) after prior inspection, information or beta from others.
Completion of a climb first try with no falls.
To successfully lead a climb you've never previously attempted - with no falls or "dogging," (ie. hanging on the rope), but with prior knowledge (beta) of its features or difficulties.
To climb a route without practice (but perhaps with beta) without falls on the first viewing and first attempt. (This is very similiar to onsight, which is even purer: no beta.) Opinion is divided as to what constitutes beta: to some people, even knowing the route's grade makes an ascent a flash rather than an onsight. Also sometimes prepended to "git" when someone achieves this feat. [Adam Palmer
to lead a route successfully on the first try; see on-sight