I am new to bioinformatics and I am currently learning how to use software that generates artificial FASTQ files from a given reference genome. In the manual appears the following:

On an Intel Xeon X5650 processor (12M cache, 2.66 GHz, 6.40GT/s Intel QPI), when using real quality scores and simulating sequencing errors, and with the other parameters set to their defaults (see Section 2), it takes about 6 hrs 20 mins to process 1 Gbase.

What exactly is a Gbase in this context?