Let's not say in WedDev only, because the cycle predates web.
Thin client - dumb terminals connected to a powerful central computer; 1960s, 1970s onwards
Thick client - multi-tier architecture, 1990s onwards, with client typically running on Windows, communicating with an application server (three tier) or database (two tier); for two tier, almost all the application logic is in the client.
Thin client - web browser communicating with web server; ~2000 onwards. The early versions are OCX controls hosted inside IE, basically hosting a Thick client as a downloadable control inside a web page, but it gradually migrates to web native as the browser gets more capable (AJAX revolution). Web native is a step change back to thin client compared to a client app or OCX control.
Thick client - this article here, a continuation of a trend over the past couple of decades, as browsers increasingly resemble operating systems in the breadth of APIs, permitting building something closer to a classic two-tier architecture, with not much more than basic validation and data backup / sync support on the back end.
Thin client - dumb terminals connected to a powerful central computer; 1960s, 1970s onwards
Thick client - multi-tier architecture, 1990s onwards, with client typically running on Windows, communicating with an application server (three tier) or database (two tier); for two tier, almost all the application logic is in the client.
Thin client - web browser communicating with web server; ~2000 onwards. The early versions are OCX controls hosted inside IE, basically hosting a Thick client as a downloadable control inside a web page, but it gradually migrates to web native as the browser gets more capable (AJAX revolution). Web native is a step change back to thin client compared to a client app or OCX control.
Thick client - this article here, a continuation of a trend over the past couple of decades, as browsers increasingly resemble operating systems in the breadth of APIs, permitting building something closer to a classic two-tier architecture, with not much more than basic validation and data backup / sync support on the back end.