Meaning:

“头” means “head,” and “985” refers to “universities included in Project 985.” In May 1998, then Chinese President Jiang Zemin set the goal of building top-rate universities to drive the country’s economic growth while speaking at a ceremony to mark the 100th anniversary of Peking University. The following year, the Ministry of Education officially launched Project 985. Therefore, a “985” university is a top Chinese university. A user on Weibo (China’s equivalent of Twitter) coined the term “985 head” to describe those, especially children, with a big forehead who appears to have a high IQ and is destined to go to a top university.

Example:

A: 你的孩子多大了？

Nǐ de háizi duōdà le？

How old is your kid?

B: 小学五年级了。

Xiǎoxué wǔniánjí le。

He is a fifth-grader now.

A: 学习一定不让你操心，我记得他长了个985头。

Xuéxí yīdìng bú ràngnǐ cāoxīn，wǒ jìdé tā zhǎng le ge jiǔbāwǔ tóu。

I guess you never worry about his academic performance at school. I still remember that he has a big forehead and looks very bright.