cursor-type

cursor-type is a variable defined in `C source code'.
Its value is

t

• Automatically becomes buffer-local when set.

Documentation:
Cursor to use when this buffer is in the selected window.
Values are interpreted as follows:

t use the cursor specified for the frame
nil don't display a cursor
box display a filled box cursor
hollow display a hollow box cursor
bar display a vertical bar cursor with default width
(bar . WIDTH) display a vertical bar cursor with width WIDTH
hbar display a horizontal bar cursor with default height
(hbar . HEIGHT) display a horizontal bar cursor with height HEIGHT
ANYTHING ELSE display a hollow box cursor

When the buffer is displayed in a non-selected window, the
cursor's appearance is instead controlled by the variable
`cursor-in-non-selected-windows'.

You can customize this variable.