If you encountered this phrase as part of a tutorial or a pop-up message, do proceed with any installation — it is almost certainly unsafe.

: Navigating the site’s dashboard to find a specific Hollywood title, then using direct links or Google Drive mirrors to download the file to a local drive.

Because 123mkv is a web-based download platform rather than a formal software application, there is no "installation" process in the traditional sense. Instead, "installing" usually refers to downloading a file and playing it on your device. How to Access and Use 123mkv

The "123" implies ease (as in "1-2-3 easy steps"), and "mkv" refers to the container format. However, the domain is frequently seized by anti-piracy agencies, forcing the operators to switch to new extensions (e.g., .net, .io, .in).