Jettison Cargo is a command available from the Cargo interface in the right UI panel which allows you to eject cargo from your ship.
There are 3 options available to jettison cargo, the availability of these options is based on the ownership status of your cargo.
Jettison Cargo is available when you have goods which is either owned or stolen. Selecting this option will eject the cargo from your ship and it will be marked "Stolen" by anyone who scoops it and can only be sold on the Black Market . (Exception: If you jettison cargo which you own and scoop it back up, it will still be owned by you.
Jettison Cargo (Abandon) is available only when you are the owner of the cargo. This means you either purchased the cargo yourself or you scooped the cargo after the previous owner jettisoned it using the "Abandon" command. This is the option to use if you want to transfer credits to another CMDR. By abandoning your cargo and letting them scoop it, they will be able to sell it on the Commodities Market .
Discard is available for owned or stolen goods when docked in a station. Please note that this will remove your cargo and it will not be able to be scooped again. Also note that if you jettison cargo while inside of a station, before docking, you will receive a fine. You need to be at least 10 kilometers from a station and outside the no-fire-zone in order to jettison cargo without receiving a fine.
After selecting the cargo, you can use the left and right UI commands to choose the amount of cargo you wish to jettison at once, up to the maximum amount you have of that type. Selecting a second time will jettison the cargo.
If you have “Haulage” cargo, which is cargo for courier missions; when you select the cargo, you will not be given any options. The only choice you would have is to deliver the cargo or abandon the mission. Abandoning the mission will change the cargo to “Stolen” and you will be fined in accordance with the mission tied to that cargo.