What does C mean at CEX?

Could you please elaborate on the meaning of the letter "C" when it's used in the context of "CEX"? In the cryptocurrency and finance industry, abbreviations and acronyms are common, and it's essential to understand their meanings. Does "C" in "CEX" stand for a specific term or concept related to cryptocurrency exchanges? Is it a universal convention, or does it vary depending on the platform or context? Clarifying the meaning of "C" in "CEX" would help in understanding the broader terminology and operations within the cryptocurrency exchange ecosystem.