It means that they have issued a warrant for his arrest for violating his probation and, since he is out of the country, they have tolled (stopped) the running of his probation time until such time as he is arrested.
What this means is that he stopped getting credit for time being served on probation as of the date of the tolling order. Thus, if he had 6 months left on probation when the tolling order was issued, he will still have that time remaining when he is re-arrested (even if it is 10 years from now). This often comes back to haunt people who otherwise behave themselves after a conviction!
If a probation warrant was issued and there was an attempt to serve the warrant ,but your friend was out of the country, and or could not be served his probation would be stopped at that time.
If/when is he is arrested his remaining time on probation could be revoked and become active jail sentence. It would be even worst if he was on First Offender probation because his probation could be revoked for the entire length of the sentence including probation time already served. He should hire a lawyer to try and minimize his situation. The longer he does not address this the worst it becomes! Good Luck!