Short answers, pulled from the story.
A financial crisis is any of a broad variety of situations in which some financial assets suddenly lose a large part of their nominal value. This definition distinguishes the event from an economic crisis, which involves a broader reduction of economic activity affecting the whole economy.
The Wall Street crash of 1929 occurred during the early 20th century and was followed by the Great Depression, which remains the largest and most important economic depression in the 20th century. The crash followed the introduction of new electrical and transportation technologies that contributed to speculative bubbles.
Frankel and Rose define a currency crisis as a nominal depreciation of a currency of at least 25 percent. Kaminsky et al. define it differently based on weighted average monthly percentage depreciations exceeding three standard deviations.
Latin American countries defaulted on their debt in the early 1980s starting with Mexico in 1982. These defaults were part of a series of sovereign defaults that fall under the category of financial crises alongside banking panics and stock market crashes.
Bear Stearns failed in 2007 and 2008 because it was unable to renew short-term debt used to finance long-term mortgage securities. This failure occurred during the subprime mortgage crisis when financial institutions experienced sudden shortages of cash or funding making it difficult to meet short-term obligations.