Yes, the dash "-" symbol is the only non-alphanumeric character allowed in standard domain names. Internationalized Domain Names (IDN) are another story, but widespread usage and browser support for them is still an issue.
IDN stands for Internationalized Domain Name. IDN is also known as multilingual domain name. This gives a possibility for using characters in domains names, besides letters, numbers and hyphens, i.e. characters available in other alphabets. For example ,accents, French, Hindi, etc.
Yep, "-", dashes or hyphens.. Whatever you want to call it is just another letter in the domainers alphabet. You are allowed up to two repeating hyphens. For example. A--D(.)com, (a name I own) and you cannot start or finish a domain name with a hyphen. Years ago this was not always the case but it is now.