What is the difference bewteen isolated and scattered thunderstorms?

As Defined by the National Weather Service

Isolated Storm

An individual cell or a group of cells that are identifiable and separate from other cells in a geographic area.

Isolated

A National Weather Service convective precipitation descriptor for a 10% chance of measurable precipitation (0.01"). Isolated is used interchangeably with few. See Precipitation Probability (PoP).

Scattered (SCT)

1. An official sky cover classification for aviation weather observations, descriptive of a sky cover of 3/8 to 4/8. This is applied only when obscuring phenomenon aloft are present--that is, not when obscuring phenomenon are surface-based, such as fog. 2. A National Weather Service convective precipitation descriptor for a 30%, 40%, and 50% chance of measurable precipitation

Scattered means that there is a 40%-60% chance of showers when isolated means there is less than 30% chance of showers. Scattered also means that small showers are scattered throughout an area and isolated means there is only one small shower in the area and your location is most likely to stay dry.