A special form of mixed-case identifiers widely used mainly in Java circles, so named because they look like this:
camelCaseIdentifier
The first word of a multi-word identifier is in lower case (the head of the "camel"), while subsequent words are capitalized (the "humps" of the "camel"). This is generally used for method names in classes, and sometimes for variable names as well. For class names, the convention is the same, except that the first letter of the class name is capitalized as well (e.g. CamelCaseClassName, cf. BiCapitalization, CamelCaps). This case convention is enshrined in the Sun Java Coding Conventions, and is used throughout the standard Java class library, so people programming in Java have come to use these conventions as well, just as the use of Hungarian notation in the Windows API has influenced code written on that platform.
Frankly, I'd prefer to use underscores for multiple-word identifiers, to allow Ctrl-arrow keys move from word to word in the name while using Emacs. Now, ariels informs me that Emacs has c-forward-into-nomenclature (and an analogous -backwards-), to forward into camelCase identifiers, but that still doesn't fix what IMHO is a more fundamental flaw with camelCase: it hurts the eyes.
The Java Coding Conventions document that describes camel case:
http://java.sun.com/docs/codeconv/html/CodeConventions.doc8.html#367