Interference is something that is in your way. If the sound of your sister's band practicing keeps you from getting your homework done, that’s interference.
Governments are sometimes accused of interference in other countries' affairs. If your neighbor’s in a civil war and your president sends in troops, your country may be accused of interference in that country's internal affairs, If all you hear on your radio is static, you’ve got interference — something is blocking the clear signal. And when a football player blocks another player, that's also interference. The Latin roots of interference are entre-, “between,” and ferire, “strike.”