Sonic lime is made with freshly squeezed lime fruit whereas limeade means sweetened lime syrup. Therefore, lime is very sour whereas limeade is already cut with sugar. A lime slush has a sour taste as compared to the sweeter limeade slush. However, Sonic has gradually been phasing out fresh lime juice to lime syrup or limeade so be sure to ask if they have fresh lime if that's what you intend to order.