\documentclass{article}
\usepackage{calc}
\newlength\foo
\begin{document}
\settototalheight\foo{\parbox{3cm}{text text text text text text text text text}}
\the\foo
\end{document}
I made the following diagram for the adjustbox bundle. It will be part of the trimclip manual (The trimclip package will be an extracted part of the current adjustbox package).
As you can see the text lies on the baseline, the height is everything above it and the depth everything below it. Usually only some lower-case character and punctuation go below it. Both together is the totalheight. Note that the coordinate system for the depth is going down, i.e. it is always positive. The width is the normal width of the content.
The macros in the document show how to access these values in LaTeX macros like \raisebox (first line) or with a TeX box register called \br here (second line).
There are further diagram which explain the trimming and clipping of boxes.
The current work-in-progress version of the manual with this diagrams can be downloaded as PDF from the code repository. The source code for this and all other diagrams are also available.
Best Answer
You can use
\raisebox
to modify the official height and depth of some text:This raises the text by 0pt (so not at all), keeps the official height identical to the original height and sets the depth to 0pt.