The practice of concatenating words with either all words capitalised (e.g. "ICantReadThis" - sometimes called "UpperCamelCase" or "PascalCase") or all except the first ("iCantReadThis" - called "lowerCamelCase"). It is used in contexts where space characters are not allowed, such as identifiers in source code.
Modern best practice separates words in identifiers with underscore for readability (like_this_example). CamelCase is probably a historical throw-back to systems that had no underscore or when the length of identifiers was constrained either by the programming language or by the width of computer displays. Unfortunately it has infected many projects, origanisations and programming languages such as Java where the uniniated create identifiers like "MemberSubmissionAddressingWSDLParserExtension".