Combining these parts, the phrase literally translates to “The Chinese Nation's Great Revival.”
The concept of `中华民族伟大复兴` is arguably the single most important ideological pillar of the modern Chinese state. Its power comes from its connection to the “Century of Humiliation” (百年国耻, bǎinián guóchǐ), the period from roughly 1839 (the First Opium War) to 1949 (the founding of the PRC) when China was repeatedly defeated, invaded, and forced to sign unequal treaties by foreign powers. This “rejuvenation” is framed as the definitive end to that era. It is a promise to the Chinese people that such weakness will never happen again.
This is a highly formal and official term. You will encounter it constantly in state-controlled contexts.