The acronym "TLD" stands for Top-Level Domain in domain names. It is the suffix at the end of a domain name, such as .com, .org, or .net, defining the domain's category or origin. TLDs are categorized into two main types: generic (gTLD) and country code (ccTLD). Understanding TLDs is vital for establishing an online presence, as they can influence perceptions of credibility and relevance in various contexts.