several hundred; hundreds (of)
Used for an approximate number in the hundreds, often with a counter or noun. Can be followed by の to modify a noun.
数百人の観客が集まった。
Several hundred spectators gathered.
Hundreds of students took part in the ceremony.
この図書館には数百冊の本がある。
This library has hundreds of books.
Hundreds of parts are assembled at the factory.
This castle was built hundreds of years ago.
数千 means 'several thousand' (roughly 2,000–9,000), while 数百 means 'several hundred', a smaller approximate quantity.
数百 means 'several hundred', while 数十 means 'several tens'—an order of magnitude smaller, so the two are easy to mix up when reading quickly.
数百 means 'several hundred', while 数千 means 'several thousand'—an order of magnitude larger, so learners can confuse the two similar-looking words.
数百 means 'hundreds', a much smaller scale than 数万, which means 'tens of thousands'.
several million; millions (of)
Compound of 数 (すう, 'several') and 百 (ひゃく, 'hundred'). The reading すうひゃく follows regular on'yomi patterns.