What does chance of thunderstorms mean

The weather man said scattered showers in the afternoon and the chance of a late thunderstorm. What is the chance of the thunderstorm happening???

Thunderstorm (TS) coverage is the percentage of area in forecast zone which may experience convective activity.

National Weather Service forecasters in the US use the term "isolated" for 10-29 percent coverage... 30-59 percent for "scattered" coverage...and 60-79 percent for "numerous" coverage. Percentages above 80 percent are described simply as "thunderstorms."

Your weatherman'a forecast for 'scattered' TSs ==> 30 to 59% of the forecast area can expect to experience a thunderstorm.

Probability for TS chances...
Slight Chance = 20%
Chance = 30% 40% 50%
Likely = 60% 70%
Occasional or Periods = 80% 90% near 100%

Weatherman's forecast for the 'chance' of late day TS ==> 20% which also implies 20% of the forecast area can expect to experience a thunderstorm.

The question is; does this particular weatherman understand the terminology and is it being conveyed correctly?

They always state things vaguely to make sure their predictions can cover even the smallest chance of some weather happening. In other words that just means there might be thunderstorms but it's not likely.

It means simply that a thunderstorm is possible, but not certain. It could happen, or it might not.

They mean that it may happen, they are not 100% sure.