What is PLR?
Private label rights usually grant some permission to edit or rebrand a product. The exact rights vary by licence; do not assume editing, resale or redistribution is automatically allowed.
What is MRR?
Master resale rights commonly permit resale and sometimes allow you to grant resale rights to customers. They do not automatically include permission to edit.
Before you buy
Read the supplied licence carefully. Check whether you can modify the files, sell on your preferred marketplace, bundle items, sublicense or redistribute source files. Ask the seller if anything is unclear.
A licence checklist you can use
Before selling any licensed product, read the included licence and confirm whether editing, rebranding, resale, bundling and sublicensing are allowed. Also check whether redistribution of editable source files is permitted.
A simple example
A seller may permit you to edit and sell a workbook but prohibit giving your customers resale rights. Another product might permit resale of the unchanged file while prohibiting edits. Both can be described informally using PLR or MRR terms, so the written licence matters more than the label.
Where to go next
Compare the product licence against the marketplace rules where you plan to sell. If permissions are unclear, ask the original rights holder before publishing.