WRC stands for World Riichi Championship. Its rules are an international competitive riichi standard published and maintained by World Riichi Limited. Tenpai.gg teaches Tenhou rules first and marks WRC differences in dedicated callouts.
The two rulesets share the general structure, main yaku, and most payments. WRC notably uses 30,000 starting points with no red fives, one ron winner, kiriage mangan, 5-han renhou, and pao for suukantsu.
A WRC note therefore does not replace the main Tenhou answer in a lesson. It prepares players for tables and tournaments that use the WRC ruleset without mixing both references.