网络(wǎng luò) - network, the internet in Mandarin

网络 (wǎng luò) is a network in every modern sense: the wifi in a flat, a company's internal systems, and the internet at large. 在网络上 is the standard way to say online.

Speech clips it hard. 上网 is to go online, 网上 is on the internet, 网站 is a website and 断网 is to lose the connection. If you only ever learn the long form you will miss most of what people actually say.

Two things to watch. 网络 is the mainland standard while Taiwan writes 网路 (wǎng lù) for the same idea, so both are correct in their own place. And 互联网 (hù lián wǎng) means the Internet specifically, so it will not do for the sluggish wifi in your hotel room.