Short for chat robot, a computer program that simulates human conversation, or chat, through artificial intelligence. Typically, a chat bot will communicate with a real person, but applications are being developed in which two chat bots can communicate with each other. Chat bots are used in applications such as ecommerce customer service, call centers and Internet gaming. Chat bots used for these purposes are typically limited to conversations regarding a specialized purpose and not for the entire range of human communication.
WeChat combines a chat-based interface with vast library of add-on features such as a mobile wallet, chat-based transactions, and chat-based media and interactive widgets, and exposes it all to businesses through a powerful API that enables businesses from mom and pop noodle shops to powerhouses such as Nike and Burberry to “friend” their customers and market to them in never before imaginable ways. Over 10MM businesses in China have WeChat accounts, and it is becoming increasingly popular for small businesses to only have a WeChat account, forgoing developing their own website or mobile app completely. US technology firms, in particular Facebook, are taking note.
One of the more talked about integrations has been Taco Bell‘s announcement that it is working on a Slackbot (appropriately named Tacobot) which will not only take your Gordita Supreme order but will do it with the same “witty personality you’d expect from Taco Bell.” Consumer demand for such a service remains to be seen, but it hints at the potential for brands to leverage Slack’s platform and growing audience.
Cheyer explains Viv like this. Imagine you need to pick up a bottle of wine that goes well with lasagna on the way to your brother's house. If you wanted to do that yourself, you'd need to determine which wine goes well with lasagna (search #1) then find a wine store that carries it (search #2) that is on the way to your brother's house (search #3). Once you have that figured out, you have to calculate what time you need to leave to stop at the wine store on the way (search #4) and still make it to his house on time.
Chatbots currently operate through a number of channels, including web, within apps, and on messaging platforms. They also work across the spectrum from digital commerce to banking using bots for research, lead generation, and brand awareness. An increasing amount of businesses are experimenting with chatbots for e-commerce, customer service, and content delivery.

User message. Once authenticated, the user sends a message to the bot. The bot reads the message and routes it to a natural language understanding service such as LUIS. This step gets the intents (what the user wants to do) and entities (what things the user is interested in). The bot then builds a query that it passes to a service that serves information, such as Azure Search for document retrieval, QnA Maker for FAQs, or a custom knowledge base. The bot uses these results to construct a response. To give the best result for a given query, the bot might make several back-and-forth calls to these remote services.
One of the first stepping stones to this future are AI-powered messaging solutions, or conversational bots. A conversational bot is a computer program that works automatically and is skilled in communicating through various digital media—including intelligent virtual agents, organizations' apps, organizations' websites, social platforms and messenger platforms. Users can interact with such bots, using voice or text, to access information, complete tasks or execute transactions. 
With the help of equation, word matches are found for given some sample sentences for each class. Classification score identifies the class with the highest term matches but it also has some limitations. The score signifies which intent is most likely to the sentence but does not guarantee it is the perfect match. Highest score only provides the relativity base.
ELIZA's key method of operation (copied by chatbot designers ever since) involves the recognition of clue words or phrases in the input, and the output of corresponding pre-prepared or pre-programmed responses that can move the conversation forward in an apparently meaningful way (e.g. by responding to any input that contains the word 'MOTHER' with 'TELL ME MORE ABOUT YOUR FAMILY').[9] Thus an illusion of understanding is generated, even though the processing involved has been merely superficial. ELIZA showed that such an illusion is surprisingly easy to generate, because human judges are so ready to give the benefit of the doubt when conversational responses are capable of being interpreted as "intelligent".