Maximise the window, or return to the previous window display size; return to the previous screen setting (CTRL-UPARROW).
Choose another Text from the list of available Buffers. The option "Add New" opens a new empty buffer. The option "Open New" turns the Text Window into a FIle Selection Window an allows to load a Text Buffer from the disk.
Give the current Text buffer a new and unique name. After the new name is entered, it appears in the list, sorted alphabetically.
The TextWindow is a simple but useful Texteditor, fully integrated into Blender. The main purpose of it is to write Python scripts, but it is also very useful to write comments in the Blendfile or to instruct other users the purpose of the scene.