To Spread Out
To Extend, To Stretch
intransitive verb, godan verb
Remember 広い? Well this is like that, except a verb. When something does the action of getting wide, it means to spread out, to extend, or to stretch.
You already learned 広げる, which is used when you spread SOMETHING. But 広がる is intransitive, so it doesn't take a direct object. Like: The sea spreads out before you. See? No direct object.
Actually, verbs ending in okurigana that rhyme with ある tend to be intransitive like this. You can remember this because if something is ある, it's just there, existing, not acting on anything else. That's why verbs that sound like it are often intransitive too!
The reading is the same as 広い, too, so as long as you knew that you knew this reading as well.
両足、もっと広がる？
Can you spread both of your legs more?
リビングルームは、この入り口から広がります。
The living room spreads from this entrance.
ウィルスは、すぐに全日本に広がった。
The virus quickly spread to all Japan.