noun
studying very hard; cramming intensely
Describes an intense, often short-term burst of studying, like cramming for an exam. Can be used as a noun or with する.
試験前は猛勉強しないと合格できない。
I have to study like crazy before the exam to pass.
彼は猛勉強の末、難関大学に合格した。
After intense studying, he got into a top university.
猛練習 means 'intense practice' and follows the same pattern of 猛 + activity noun.
Compound of 猛 (もう, 'fierce, intense') and 勉強 (べんきょう, 'study'). The prefix 猛 is used in similar compounds like 猛練習 (intense practice) and 猛暑 (intense heat).