This is just a single "E" string from the Pirastro Passione line. It is a heavy gauge string for a standard four-string bass.
Pirastro Passione bass strings for orchestra playing give you clean string changes, quick articulation, response to heavy and light bow strokes, good dynamic range and warm, medium tone color. Our observation is the character of Passione strings is most compatible with fine double basses. The players who seem to get the most out of them and stick with this brand have them on older basses, and depend on them for high-level orchestra playing.