This is a Mute icon. We've made it in iOS style, first introduced in iOS version 7 and supported in all later releases up until now (at least iOS 11). This style is based on thin two-pixel lines and is optimized for 50x50 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 12,300 icons, all in the same style and quality.
It is a classic mute icon. There is a basic speaker with the letter "x", or what could be a cross icon to the right of it. You can clearly see the back and front of the speaker. You would not think sound is coming out of this speaker.