The definition of makeshift is something that is improvised or serving as a substitute.
If your window is broken and you stick a piece of Plexiglass up as a temporary solution, this is an example of a makeshift window.
a thing that will do for a while as a substitute; temporary expedient
that will do for a while as a substitute
Suitable as a temporary or expedient substitute: used a rock as a makeshift hammer.
A temporary or expedient substitute for something else: lacked a cane but used a stick as a makeshift.
(comparative more makeshift, superlative most makeshift)