What is the meaning of the phrase Mustard on the Beat Hoe on the introduction of many rap songs?

Meek Mill Lyrics
“Whatever You Need”
(feat. Chris Brown & Ty Dolla $ign)

[YG:]
Mustard on the beat, hoe… This introductory catch phrase used on many hip-hop songs has 4 meanings and uses:

1.- It is the catch phrase used by DJ Mustard on many of their own songs and remixes.

2.- Many other artists like Meek Mill, Chris Brown, Ty Dolla $ign use this phrase on their hit songs but always in the beginning of those tunes.

3.- It means to do something fast and swiftly

4.- Also it is use to connote other phrase: The Cherry on the Cake which means this song is gonna be a hit.

[Chris Brown (Ty Dolla $ign):]
Girl, as long as you, wrap your arms ‘round me
Ooh baby, I don’t care what them people say
I’m givin’ you whatever you want
Girl, you know I can provide
Whatever you need
(Whatever you need, babe)
Listen to your heart, baby

[Meek Mill:]
Yeah, I’m the only young nigga who’s poppin’ that
Got it jumpin’ out the heat there like who coppin’ that?
New G Wagon got her braggin’, put a lock on that
Niggas always hit her DM, she don’t holla back, woo, woo, copy that
Cuffin’, I’ve been cuffin’
Chanel bags like it’s nothin’, and she love them
Her last nigga, he was bluffin’, she said, “Fuck him”
He let that go, I’m like, “He buggin’,” now she thuggin’ with a real one
I’ve been ballin’ on you ‘cause you smart and loyal
All my homies know me best, they say I’m fallin’ for you
And that box be slippery like tryna walk on oil
And I’ll be there long as you there when I be callin’ for you, facts

[Chris Brown (Ty Dolla $ign):]
Girl, as long as you, wrap your arms ‘round me
Ooh, baby I don’t care what them people say
I’m givin’ you whatever you want
Girl, you know I can provide
Whatever you need
(Whatever you need, babe)
Listen to your heart, baby

[Meek Mill:]
Yeah, you can get whatever you want, whatever you need
Got a one way flight ‘cause I ain’t lettin’ you leave
We ain’t fuck first night, had me beggin’ you please
But you love when I’m beggin’, you told me get on my knees
And I ate it, we got faded
You said, “Put some Tory Lanez on” and I played it
In Philly, we say you the main joint and we save it
Finally got a rich nigga, baby, you made it
Long as you hold me down, you know that it’s goin’ down
Be there when I turn around and I’ll turn your world around
I had to tone it down ‘cause you made me slow it down
But I got you open now, so I’m ‘bout to show you now, show you now

[Ty Dolla $ign:]
What makes you think that I would try to run a game on you?
Just as sure as my name is Dolla, I’ll be there for you and I’ll
Treat you just like a queen and give you fine things
You’ll never have to worry ‘bout another in your place, so believe me when I say