Tracks in your library can be locked to avoid accidentally changing the BPM or Beatgrid information for the file. This provides a handy visual aid for tracks in your library you feel have correct Beatgrids and BPM values. Find a track you wish to lock, hold control + click in the empty Status column (the first column in the main Library view). A Blue Lock icon will be displayed in this field. Press control + click again on this icon to unlock the track.
TIP: You can lock several tracks at once. Highlight the track selection you want and then click in the Status column. Serato DJ will then prompt you if you want to edit all the tags for these tracks.