Viewing '-' from the fight menu.
"-" refers to the 'move' with an index number of 0, as it appears in Pokémon Gold, Silver and Pokémon Crystal. When it is the first move in a Pokémon's list of moves, it is accessible as a glitch move.
The name "-" was taken from what it is called on the status screen and the fight menu. This name is used in regular gameplay for blank move entries.
Opening the fight menu with this move may result in a freeze, but other times it is usable.
Accessing the glitch move
"-" as the first move can be obtained by trading a Pokémon with - (Generation I move) as the first move over from Pokémon Red, Blue, Yellow to Gold, Silver or Crystal. This can be done with the swapping Transform moves glitch, which is most easy to pull off by getting a Ditto.
Effect and type
In Pokémon Gold, Silver and Pokémon Crystal the move is a status move that induces bad poison and is Normal-type according to the fight menu, but its accuracy doesn't seem to be too good.