This is the 752nd most frequent Turkish word.
ulusal
"Ulusal" means "national" in English.
Here, 'ulusal' is used as an adjective describing the flag as being associated with the nation.
Türk bayrağı ulusal bir semboldür.
The Turkish flag is a national symbol.
In this sentence, 'ulusal' qualifies the television channel, specifying it as belonging to or representing the nation.
Ulusal bir televizyon kanalında bu haberi gördüm.
I saw this news on a national television channel.
The word 'ulusal' here serves to describe parks that are designated as part of the nation's natural heritage.