Plural or genitive (=possessive) form of the latin word Reticulum (meaning 'network').
Reticuli is often used as a synonym for the Zeta Reticuli, or Zetas, i.e. the inhabitants of the Zeta Reticulum Rhomboidalis 1 and 2.
See "Zetas" for explanation.
This topic was copied from the HyperBase and is likely to be revised.