1. A space in between two of the same objects, where part of a chain or object is missing, or where certain activities, processes, or events are lacking. A period of time characterized by a lack of activity, in between two events or within a continuous process.
  2. In molecular biology or genetics, a gap is a spot on a strand of DNA or RNA where a nucleotide or a segment of nucleotides is missing.

From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.