Typing is the use of a keyboard
to produce text
With the ubiquitousness of computing equipment, typing has become a vastly more effective way to communicate language than handwriting in most circumstances. It is easier to learn and easier to use, for both reader and writer. Handwriting is not considered to be more expressive than typed text; all it can add is charm and a sense of style, or other aspects (a glimpse at the author's state of mind) that are not considered part of the message.
Speech on the other hand is considered more expressive than any form of written text. A tone of voice, intonation, timing and many other aspects can be used do add meaning to language. Linguistics still considers itself to be have the spoken word as its object of study - written text is largely considered to be a condensed form of speech. This really isn't correct: typed language dvelops all kinds of forms of expression on its own without any counterparts in speech. But it cannot be doubted that the spoken word will continue to be more expressive or convenient than the written word in many siuiations of use, and it can also be learnt at a much younger age. So we can safely say that the typed word will continue to grow in importance, but will never come near to replacing it altogether.
In formal language theory, typing is the classification of datas into types that restrict their possible use: operations and functions work on values of a specific type. This is particularly important for programming languages.
In strong typing, the type checking is performed statically: it can be done at specification time. In dynamic typing, type checking is (partly) performed at runtime, that is, typing errors may be discovered while the program is executed.
Different languages vary in their degree and strictness of typing. Generally speaking there is a tradeoff here between the power to catch errors and the power of flexible use.