height of; middle of; full bloom
Describes the peak or most intense period of something, often used for seasons, events, or conditions. Can also mean the middle of a period. The gloss 'full bloom' is a specific application to flowers.
It's the height of summer now.
桜が真盛りを迎えている。
The cherry blossoms are in full bloom.
Formed from the intensifying prefix 真 and 盛り “height, peak,” denoting the very height or fullest stage of something.