last spring; the spring of last year
A straightforward temporal noun/adverb meaning the spring of the previous year. Used in both formal and everyday contexts.
昨春、この公園に桜の木を植えました。
Last spring, we planted cherry trees in this park.
He graduated from university last spring.
The event last spring was a great success.
昨春から新しい仕事を始めた。
I started a new job since last spring.
今春 refers to this spring, whereas 昨春 refers to last spring, the previous year's spring.
Compound of 昨 (saku, 'last, previous') and 春 (shun, 'spring'). The reading is the on'yomi of both characters.