A semi-Snark is any small stable signal conduit that produces one output glider for every two input gliders, with a 90 degree reflection. These can act as period-doublers for any glider stream whose period is at least equal to their repeat time, and so adding one of these to a single glider gun often results in a pattern much smaller than the older technology of crossing the output of two guns.
The available semi-Snarks differ in their complexity, size, repeat time, and the colour of their output gliders. The CC semi-Snark was the first one found, and the term "semi-Snark" is often used specifically for this object. The "CC" prefix stands for colour-changing, by contrast with the more recently discovered colour-preserving CP semi-Snark.
There are also CC and CP variants of a semi-Snark based on a two-glider to century converter discovered by Tanner Jacobi in November 2017. These semi-cenarks are the fastest semi-Snarks known as of the end of 2017, with a repeat time as low as 50 ticks, or a periodic input rate as low as 36 ticks.