Top up Definition 1 of 3Pro Tip 1/3Technological Context Often used with phones or online accounts where credit is consumed and must be replenished. My data plan ran out; I need to top up. Pro Tip 2/3Prepaid Services Associated with services you pay for before use, like prepaid mobile plans and gift cards. My subway card is low on funds, time to top up. Pro Tip 3/3Casual Phrase Common in everyday speech, particularly among younger people, when discussing credit or funds. Let's top up online before we go shopping.