1 : a part of a larger amount, area, etc.
A portion of the donations will be given to the orphanage.
Portions of land were used for farming.
A considerable/significant portion of the city was flooded.
2 : a part of something that is shared with other people — usually singular
A portion of the blame belongs to you.
He took on a large portion of the work.
3 : the amount of food that is served to a person at one time
The restaurant gives large/generous portions.
I'll just have a small portion [=serving] of meat.
She divided the pie into six equal portions.