What is the definition of a motif in biochemistry?

A series of amino acids associated with a specific function, contiguous or aligned with respect to certain invariant or conserved positions of the primary sequence of a protein.
A conserved sequence of six nucleotides recognized by the sigma initiation factor of transcription initiation in prokaryotic promoters.
A polymer of nucleotides linked by 5'-3' phosphodiester bonds of length greater than 50 units.
An RNA polymerase specialized in DNA replication that catalyzes the formation of small RNA fragments (primers) on one of the DNA strands that serves as a template.