What is the difference between mark-up and margin?

We're selling wholesale sausages to a retailer. We sell them to the retailer at £5 a sausage. They sell them at £10. Why would the retailer work out the markup and margin — what would the different numbers mean to me, and the retailer?

This is a follow-up question to What is the difference between gross and net?.

Can anybody tell me the difference between Used Margin and Usable Margin?And when we will get a Margin call either when our Losses are bigger than Used margin/usable margin?

For example...I am a distributor and I buy an item for $1.00......should I sell it for $1.20 (which is 20% markup) or should I sell it for $1.25 which is a 20% profit margin... What is a general rule of thumb for marking up candy products? What type...

If you say 5X markup/80% margins (as an example), you could mean that you sell it to the distributor for 5X markup, or you could mean that it ends up getting marked up 5X by the time it gets to retail with multiple markups along the way, but you probably...

For GMP, the formula is GMP=(Price-Cost)/Price; Markup=(Price-Cost)/Cost and the difference is denominator, but why people derive this very two similar concept? To me, Markup makes more sense because it means how much profit you make per one product.