What is the meaning of "上火“？

Generally, it has 2 meanings:
1. oral Chinese: to get angry eg.这个小孩没礼貌，真让人上火。
2. medical term: to suffer from excessive internal heat eg.嘴唇起泡，上火了 Got cold sores on one's lips due to excessive internal heat

It means endocrine dyscrasia. You get angry or sad and your body feels like fire.

To get angry
It's a verb

As an adjective, you can understand it as anger. For example, "He made me angry" also can be said like"He made me 上火"。

It is a verb and it's related to Chinese Traditional Medicine. 上火 means there's too much inner heat in the body to cause discomfort (not necessarily sick).

to get angry

Get angry

上火 - Verb
For example - 这事真让人上火。

“上火”is a fixed word, also is a verb.
Have two meanings:
1.Traditonal Chinese medicine (中医）
for example：
我上火了，牙痛。
我上火了，眼睛不舒服。
2.to get angry.
for example：
他的行为，让人很上火。
为一点小事，犯不着上火。

to get angry