Enter portion of Ohio adjusted gross income that is subjectedto tax by another state or the District of Columbia.what does this mean in simple terms?

Did you get a W-2 for your job in PA?  If so, did it show any PA state taxes withheld?

Simple answer: the business income. 

PA & OH have a reciprocal agreement on wages. Your wages are not taxed by PA.  But, the reciprocal agreement does not apply to self employment income. 

If you  earned business income by working in PA, you have to file a PA return to pay PA tax on the portion earned in PA.  OH will give you a credit or partial credit for the tax paid to PA.   

If you mistakenly paid PA tax on your wages, OH will not give you a credit for that. You have to get it back from PA.