Quick meaning
Old software that is still in use even though newer versions exist, often because switching is complicated.
Think of it like this
Like still using a reliable old fax machine in an office because the system was built around it.
Where you may see this
You may see this inside app stores, app settings, software updates, and install instructions.
Why it matters
Knowing the term helps you understand what an app is asking you to do before you tap, install, or change anything.
Say it simply
Legacy Software means: Old software that is still in use even though newer versions exist, often because switching is complicated.