"Talk" is almost biological. It just means making words with your mouth. The words don't even have to make sense. Nobody needs to be listening. You can talk in your sleep, and some people do. "Chat" is easy going informal conversation. "Speaking" is very close in meaning to talking but usually tends to be more formal and respectful. Thus, when you pick up a telephone, you answer by saying "This is Ilya speaking". Don't ever say "This is Ilya talking" because it sounds awkward. A lecturer is called a "speaker" and it is more dignified to say he is "speaking" to his audience, rather than "talking" to them. It's ok to say he's talking to them but it sounds less formal. Another difference is that "talk" is also a noun, whereas "speak" is not. So if a lecturer is speaking/talking to an audience about butterflies, you could ask "What is that man speaking/talking about?", and the answer would be "He's giving a talk about butterflies". You could also say "He's speaking/talking about butterflies" and both words would be equally good.

CHAT IS AN INFORMAL CONVERSATION LIKE:- WITH FRIENDS , FAMILY ETC WE CAN CHAT THROUGH TEXT MESSAGES BUT TALK IS AN FORMAL CONVERSATION. IN TALK CASE WE TALK ABOUT A PARTICULAR TOPIC . WE TALK THROUGH SPOKEN LANGUAGE, WE CAN'T TALK THROUGH MESSAGES

hi guys

SH_O_BO is correct about the formality of chat vs. talk. Typically chat implies a quick discussion about something not very serious. You could chat with family, friends, coworkers, even your boss. Chat also indicates there will be back and forth dialogue in the conversation. Another common term that conveys the same tone as chat is the word visit. "Come by and we'll visit about that." means a pretty unimportant topic is being discussed. When someone says they need to talk to you or speak to you, there is a more formal tone to the conversation. Talking with someone can be casual, but tends to be more formal and business oriented. If someone says they need to speak to you, the topic is usually urgent and serious. Also, talk and speak are both used to convey a one way conversation, such as a lecture. Example: The professor spoke about the condition of trade relations between the two countries. No one would ever use chat in this scenario.

To chat is casual. You would chat to a friend when you are having coffee together. You might chat to your mum on the phone about her birthday. You wouldn't "chat" to a police officer :P To talk is more general. Every time you have a conversation, you're talking. If you say "I had a talk with..." that implies a more serious conversation, however. You would talk to your doctor about a worrying ailment, or have a talk with your child about bad behaviour. But generally, talk only has these connotations in specific contexts. Finally, to speak is, more often that not, referring to the physical act of speaking. You might say "I spoke to..." but that's quite formal. You might say "I speak with difficulty", "he speaks with an accent"... so you'd commonly use "speak" when talking about speaking itself.