记性 (jì xing) refers specifically to one's memory as a faculty or capacity — how well you can remember things. It contrasts with 记忆 (jì yì), which can mean the act of remembering or the stored memories themselves, and with 印象 (yìn xiàng), which is the impression something leaves on you. Use 记性 when talking about someone's ability to retain information (e.g., 'good memory').