It is believed that this phone call will greatly anger China, as it considers Taiwan to be a renegade state.
China has hundreds and hundreds of missiles pointed directly at Taiwan, and insists that Taiwan is apart of China under their strict "One-China Policy". This "One-China Policy" has declared that there is only one China and Taiwan is only one part of China.
The USA broke official ties with Taiwan in 1979 in support of the "Once-China Policy". However, the USA has maintained friendly, yet unofficial ties with Taiwan since then.
During the call, President-Elect Trump also congratulated Ing-wen, Taiwain's first female president, on her landslide victory in the Taiwanese presidential elections in January 2016.
Trump's transition team also said that the President-Elect reaffirmed the USA's and Taiwan's "close economic, political, and security ties".
to sever - to cut
renegade - someone / group that leaves the main group; a runaway
landslide - a win by a very large amount (margin)
transition team - a group of people who work for the next president to prepare for his office
transition - a change
reaffirm - to state again as being true