Reticulating splines (including many derivative forms) is a phrase included in many Maxis games (or their non-Maxis successors), including SimCity (SimCity 2000 and later), SimCopter, The Sims, The Sims 2, The Sims 3, and The Sims 4. The phrase is most often shown in text while on a loading screen, though it was spoken aloud in its first appearance in SimCity 2000. The term has become a somewhat well known in-joke and reference to SimCity or Maxis games in general.
The words 'reticulate' and 'spline' both have dictionary definitions, which has led several people to determine a meaning for the phrase, such as "to make a network of curved elements." However, Will Wright stated in an interview that the term itself is meaningless, as SimCity 2000 does not reticulate splines when generating terrain; the phrase was included in the game because it "sounded cool." It has since been included in many Maxis games, mostly for humor, much like the references to llamas in multiple games.
Usage outside of Maxis games[]
Technical explanation[]
A spline is a mathematically defined curve. If you've ever used an art tool that allows you to draw with vector shapes (the kind that have two points that mark the ends and then two 'handles' that define the direction of the curve at those ends), you've come across splines. Those ones are Bézier splines, but there are other types with different maths behind them that serve different purposes. Google the phrase 'flat spline' if you want to see the nifty mechanical device that the word comes from, but nowadays (and especially in a programming context) it's about the mathematically defined curve.
The term 'reticulate' seems to have a broader meaning, but it means something along the lines of 'to divide something into smaller connected parts'.
Because modern graphics hardware deals mostly with straight lines and triangles, you can't draw a curve like a spline 'directly' - you render it by evaluating the position at lots of points along the spline, and then drawing short straight line segments to connect those dots (kind of like how a game can approximate a sphere with lots of triangles). So reticulating a spline would be the process of evaluating the points along a spline, so you've broken it up into short line segments to render it.
That's what it would mean if it meant anything.
Source: Dinaroozie on Reddit r/programming