From FIXwiki

Side Value 4

A round-lot market order to sell -plus- is an order to sell a stated amount of a stock provided that its price is:

- not lower than the last sale if the last sale was a -plus- or -zero plus- tick and

- not lower than the last sale minus the minimum fractional change in the stock if the last sale was a -minus- or -zero minus- tick.

A limit-price order to sell -plus- also states the lowest price at which it can be executed.

Notes

Error in FIX Specification:

In the Glossary (Spec volume 1) this value is incorrectly associated with the OrdType field.