truncate-lines

truncate-lines is a variable defined in `C source code'.
Its value is

nil

• Automatically becomes buffer-local when set.
• This variable is safe as a file local variable if its value
  satisfies the predicate `booleanp'.

Documentation:
Non-nil means do not display continuation lines.
Instead, give each line of text just one screen line.

Note that this is overridden by the variable
`truncate-partial-width-windows' if that variable is non-nil
and this buffer is not full-frame width.

Minibuffers set this variable to nil.

You can customize this variable.