"csgoct" typically refers to the common (formerly CS:GO) chat emoticon :csgoct: . This emoticon is a reward for crafting badges from Steam Trading Cards and depicts the Counter-Terrorist (CT) icon.
Based on common CS:GO terminology, here are the most likely interpretations: csgoct
If you have a named csgoct.dem :
If you are simply a fan of the 10th Birthday event and want something in-game rather than a physical trophy: "csgoct" typically refers to the common (formerly CS:GO)