POS Software: "Point of Sale", which is generally an oversimplified view that a company's software only needs to handle what happens at the checkout counter.
ERP Software: "Enterprise Resource Planning", which is generally an overly complicated idea that one software package can do every single thing your company that spans multiple countries.
While these categories of software are different, one of the biggest differences is just who they're marketing to. POS gets sold to small stores. ERP gets sold to big corporations. Both of them handle "selling an item". Some POS also handle bookkeeping/accounting. ERP will have bookkeeping/accounting as well as handle areas like inventory and purchasing. Some ERP will add employee payroll or manufacturing process abilities.
The bottom line here is that it's much more useful to think of business software as a range rather than two distinct categories. Alox sits right at the spot where you're focused on getting sales out the door at your stores, but realize that you need "all the rest of it" to be in there also. Purchasing from your vendors, doing inventory counts, getting the sales tax back to the state, getting the nightly deposits squared away... it all needs to be at your fingertips.