Next time please give a minimal working sample.
I advise you to use the description
environment which could be revised to get the desired output by the enumitem
package. See the following MWS. By the way, it's better to delete the colons (:
) after the label words.
\documentclass{article}
\usepackage{enumitem}
\begin{document}
Some texts.
\begin{description}[leftmargin=7em, labelwidth=7em, labelsep=0em]
\item[Array:]
Fixed size vector of other type-objects.\newline
All type-objects contained must be of the same type.
...
\item[BasicType:]
All scalar types of C (int, double, unsigned short, char\ldots).\newline
Represented as a fixed-size vector of bytes.
\end{description}
Some more texts.
\end{document}

At last, let me explain different uses of the enumerate
, itemize
and description
environments: (1) enumerate
lists items with orders, and so is used for ordered lists; (2) itemize
lists items without orders, and so is used for unordered lists; (3) description
lists items with or without orders and with contents to explain the label words, and so so is used for descriptive lists.