It means that they plan on visiting sometime between now and when the year ends. This means that it could be anywhere from August through the month of December of this year. Usually, though, when a person says 'later this year', they are not talking about the immediate future - next week, for example. The impression I would get if somebody said 'later this year' would be September through December of this year, though it is not definite. The description 'later this year' is vague - intentionally, because the speaker may not have made definite plans as to time.

i with agree sarina

you can say -later today -later in the week -later this month -later this year its all very vague but its to set a time frame when something will happen or take place at a different time. not necessarily having to be in the near or far future.

It means another time through this year.