It's called ultraviolet rays.是什么意思？

It's called ultraviolet rays.

它被叫做紫外线.

called

v. 叫( call的过去式和过去分词 )，通电话，认为，估计；

例句
He has also called for an acceleration of political reforms.
他同时呼吁加快政治改革的步伐。

ultraviolet

adj. 紫外的，紫外线的，产生紫外线的；n. 紫外线辐射，紫外光；

例句
The container is invisible until you shine an ultraviolet light on it...
那个柜子只有用紫外线照射才可以看见。

rays

n. 微量( ray的名词复数 )，光束，（热或其他能量的）射线，大调音阶的第 2 音；

例句
It's safer to fake a tan with make-up rather than subject your complexion to the harsh rays of the sun...
用化妆品打造出古铜色的皮肤比让皮肤受太阳的暴晒更为安全。