Short answers, pulled from the story.
The Czech lands is a historical-geographical term for three regions: Bohemia, Moravia, and Czech Silesia. Together they formed the Czech part of Czechoslovakia from 1919 and became the Czech Republic on the 1st of January 1993.
The official non-auxiliary term in Czech geographical terminology for the present-day Czech lands is Česko. The word is documented as early as 1704, though at that time it referred only to Bohemia.
Charles IV became King of the Romans in 1346 and later Holy Roman Emperor. He incorporated Silesia and the Lusatias into the Bohemian Crown and confirmed their indivisibility from the Holy Roman Empire. In 1367 he also purchased Lower Lusatia.
Prussian king Frederick the Great conquered the bulk of Silesia in the First Silesian War of 1742, during the War of the Austrian Succession. Habsburg queen Maria Theresa lost that territory as a result.
Both Lusatias passed to the Electorate of Saxony through the Peace of Prague in 1635, during the Thirty Years' War. King John the Blind had acquired Upper Lusatia in 1319 and 1329, and Charles IV added Lower Lusatia in 1367.
The coat of arms of the Czech Republic incorporates the arms of Bohemia, Moravia, and Czech Silesia. Bohemia's arms came from the Kingdom of Bohemia, Moravia's from the Moravian margraviate, and Czech Silesia's originated as the symbol for the full historical region of Silesia, much of which is now in Poland.