转账 means 'to transfer money' between bank accounts. It's a separable verb (离合词): the verb 转 and the noun 账 can be split by aspect markers (了, 过) or measure words (一笔, 一次, 一万元). For example, 转了一笔账 ('transferred a sum of money') or 转过两次账 ('have transferred twice'). You can also add a recipient with 给: 转账给他 ('transfer money to him'). The word is commonly used in banking and mobile payment contexts.