BPM and key are the two technical numbers any DJ checks before mixing two tracks together.

BPM

Beats per minute. The tempo. DnB is 174 BPM (approximately, with some drift up). Two tracks at the same BPM beat-match cleanly. Tracks at different BPMs require tempo correction or rhythmic restructuring during the transition.

Key

The musical key the track is in. Most DJs aim to mix between tracks in compatible keys (the same key, or one a fifth or fourth apart) so that basslines and melodic content do not clash. The Camelot Wheel is a common chart for figuring this out quickly. Most modern DJ software displays key automatically.