Yahoo was the internet destination back in the 90s and into the 2000s until Google started to eat their lunch in search and email.
In my opinion, Yahoo's strength was its diversity; it was a one-stop shop for everything internet. You could register domain names, set up web pages, sell items, conduct email, instant messaging, etc. all within the yahoo.com domain. Gradually, it seems that other, nimbler competitors have gradually chipped away at Yahoo's lead until it seems they don't do anything particularly well compared to the competition. Too bad.
They still do have 400 million email users, and email users are loathe to change, so that business is probably safe for a while. But with nothing new to offer, and many good offerings sinking or gone, Yahoo is becoming a low price acquisition target. Sad to watch; at one time it was the iconic Internet business, in the Fortune 500, that could seemingly do nothing wrong.