The noun 时光 (shíguāng) means "time" or "period of time" and carries a slightly poetic or nostalgic nuance. It is often used when reflecting on past experiences or describing memorable periods, and is more literary than the everyday word 时间 (shíjiān).
大学时光是我最难忘的日子。
dàxué shíguāng shì wǒ zuì nánwàng de rìzi.
My college years were the most unforgettable days of my life.
和你在一起的时光总是过得特别快。
hé nǐ zài yīqǐ de shíguāng zǒngshì guò de tèbié kuài.
Time always seems to pass especially fast when I'm with you.
他常常怀念在农村度过的童年时光。
tā chángcháng huáiniàn zài nóngcūn dùguò de tóngnián shíguāng.
He often misses the childhood years he spent in the countryside.