In software industry, while naming a new app or a product, will there be any copyright issue if we use an existing name?
The term in your question, "use an existing name", is pretty broad.
Do you propose to say, "Compatible with Microsoft Lync"?
Or will you actually name your product "Lync"?
The first option is likely safe. The second one looks like a Trademark infringement more than a copyright issue. And "Lync" is distinctive enough, you probably won't win.
However, if you propose to name your product "Messenger", you're slightly better off because "messenger" is a generic term in the English Language, even if Facebook adopted it for their product.
The major criteria would be if your chosen name is likely to cause confusion with Facebook's product.
The names of software programs and apps, like the titles of books and movies, are not protected by copyright. However, they are often protected as trademarks. If a new product uses the name of an existing product, or part of it, or a significantly similar term, or a visual symbol such as a logo, such that a reasonable person might be falsely led to believe that the new thing is made by, endorsed by, approved by, sponsored by, or in some way affiliated with the makers of the existing thing, that might well be trademark infringement. If a reasonable person might be confused about the source, approval, or endorsement, that could also be infringement. It will only be infringement if the name (or symbol) of the existing product is protected as a trademark.
The rules for obtaining protection are different in different countries. In some countries, merely using a name or logo in commerce will grant at least some protection. In other countries, some sort of official registration is required for any protection to apply.
It is generally permitted to refer to another product by its name for purposes of comparison or review or similar reference, provided that no "passing off" a product as being from or affiliated with the makers of the other product is being done, and no confusion is probable. This is known as nominative use. For example:
- Compatible with Acme Corp's WordMaker.
- 50% faster than Acme Corp's WordMaker.
- Half the price of Acme Corp's WordMaker.
would all be permissible. A prominent disclaimer, such as "This product made by Zebra Corp, and is in no way sponsored by, endorsed by, or affiliated with Acme Corp. "WordMaker" is a trademark of Acme Corp." helps to make sure that no reasonable person would be confused.
Note also that use of a name out side of commerce, that is in no way connected with selling or advertising a product or service is generally not subject to trademark protect. But again, the law on this varies in different countries.
Note also that a name or other mark that is not distinctive will receive little or no protection. I could open a shop called "David's Best Pizza", but I would probably not win a trademark suit against a shop called 'Tom's Best Pizza", as "Best Pizza" is not very distinctive.
Note also that trademarks are generally protected only in the industry and geographic region where they are used. A product called "Dolphin Pizza" sold in New York would likely be protected in New York, and perhaps New Jersey, but probably not in California. And that trademark probably would not be able to prevent someone from using "Dolphin" as the name of a line of pools, or showers, or computers. However, at least in the US, "Famous" marks which are widely recognized get wider protection. The mark "IBM" might be protected even in industries that IBM has never marketed any product in, for example.