I hear Latin and Sanskrit are called dead languages. Sanskrit is used in rituals and at the temples. I think this is also true of Latin. What is the cause of their degradation when they have enriched so many languages like English and Telugu which are expanding on a large scale, especially English across the globe?
By definition, a dead language is a language that does not have any native speakers anymore but that had native speakers earlier (the last clause is needed to delineate dead languages from constructed languages that never ever had any native speakers). Looking at the definition, Latin is definitely a dead language, and Sanskrit is a dead language, too, despite some revival experiments (see Is the Sanskrit spoken natively in pockets in India changing? for more info on Sanskrit revival).
The definition of a dead language does not preclude its use in religion, science, or even administration, it does not diminish its prestige, and it does not make a language unsuitable as a donor of borrowed words in other languages.
EDIT: It is also possible that L2 learners of a dead language use it for communication or for composing literary works (There is a Latin translation of Asterix, after all)
In my understanding, living languages grow and change as people use and experience them. There's technical terms formed as new techniques are discovered, slang created as people, kids, want to be cliquish and edgy and not-quite-understood, shifting words and phrases and meanings as people want to speak about something without outright saying it, right? Some definitions say a living language needs native speakers, I think it has more to do with casual speakers - I think it matters more if they use the language for daily conversation rather than at what age they learned it. Languages in constant use change as the people using them change, with loan words and technical terms, with phrases and terms used by stories or anecdotes, with terms becoming popular or falling out of use, with cultural shifts over what to say and how, or what not to say and how.
Dead languages don't have that, they are static, unchanging. They can be used, even used often, (this distinguishes them from extinct languages), but because they aren't used casually and for day-to-day stuff, they don't change, not really. You mention rituals and temples, well, this is an example - you don't usually get people making up new words or phrases in the middle of things, or changing meanings or shifting things around just because - religious rites and rituals are meant to be constant and unchanging, the words and meanings should be the same every time to invoke continuity and honor the strength of the past. The same is true of other uses of dead languages, academic uses like medical latin, translation of literature from that language, use of quotes or set phrases (phrases whose meaning is independent of the actual words being used).
There are languages that have moved back across that border, revived languages, jknappen mentions attempts at reviving Sanskrit, and I believe Hebrew and Cornish both revived to living languages as people both learned them and made an effort to use them communally. There are also languages that are endangered, which furthers the metaphor for the line between languages in common use and those whose usage has declined to formal contexts alone - languages we fear might go the same path and lose vitality as the population that was using these languages, and the culture that shaped it, diminish and become assimilated to other cultures. Because there is a difference between the languages whose meanings are found in people's conversations, and the ones whose meanings are found in books.
Calling a language dead isn't meant to deny its history or all the things it has inspired or shaped, or minimalize its current use, the term is used to note that the uses are different when a language is not being used in day-to-day life, that it is no longer used casually or flexibly, but remains constant and formal, that it remains preserved for certain uses instead of growing and changing on its own.
I can't say anything about Latin but I can definitely tell you something about Sanskrit. Sanskrit is a less spoken language not a dead language. There are 7 villages in India where all the people including small children, women,elder people, literate and illiterate speak fluently in Sanskrit:
- Mattur (Karnataka)
- Jhiri (MP)
- Sasana (Orrisa)
- Ganoda (Rajasthan)
- Mohad (MP)
- Hosahalika (Karnataka)
There is one more village in Bihar where Sanskrit is a primary language but I don't recall its name.
Sanskrit is a very scientific language. The next generation super computers are planned to be made in Sanskrit language as NASA believes it is the most easily understandable language by computer. But in India, the government didn't promote this wonderful language; that's the reason why it comes to end in most of the states. Maybe in the next few decades it will become a dead language but presently it's not.