Tertiary stress is mostly applicable to words of four or more syllables
, and refers to the stress placed on the third syllable from the end of the word.
For example, the word "university" has five syllables and tertiary stress on the third syllable from the end - /ˌjuː.nɪˈvɜː.sɪ.ti/.
Tertiary stress is not as prominent as primary or secondary stress, and is often not indicated in dictionaries or pronunciation guides. However, it can still affect the way a word is pronounced and understood, and it's important for non-native speakers to be aware of it in order to communicate effectively.