A block of text is defined as a section of text that can be selected. This selection preludes the performance of a specified task with the block. Such tasks include, editing, copying and pasting, moving the text to another location within the document or to another document, or deletion of the block of text altogether.

The text block that is selected is highlighted on the computer screen using the mouse. In a Windows environment the cursor is directed to the beginning or the end of the target area of text and the desired text highlighted. Typically this is achieved by depressing the left-hand key of the mouse or mouse pad (although the mouse can be configured so that the right key or portion of the pad is depressed) at the same time as the cursor is dragged by the mouse to mark the other boundary of the block. The appropriate mouse button is then clicked to define the block of text.

The ability to manipulate a block of text is a fundamental component of word processing programs. In addition, the definition of a block of text (sometimes the text contained with a table entry or a page) allows importing and exporting of text to other programs that may further process the text or graphical data (i.e., transition of text to graphics (e.g., .tiff files) or the reverse process whereby optical character recognition programs (OCR) programs) turn fax or graphical representations into text that may be used by word processing programs.