Is Open Source Software Legal To Use For My Business?

I can download and keep using free and open source software (FOSS) on multiple computers. Is this software legal to use for my business? Can you provide some legal information regarding usage of open source software for business which I can share with my boss?

Short answer - yes.
Free and open source software is legal for both personal and business use. FOSS comes with a free license such as GPL (e.g. Linux kernel). Other application software comes with a slightly different license. You will find license information on projects website itself.
There is one very simple rule that you should follow while using FOSS for business or personal use:

Do not take source code you did not write and try to sell it as your own software, period.

I'm not a lawyer but above is simple rule to follow. Please see the following resource for more information:

• FSF Free Software Licensing and Compliance Lab
• The Open Source Definition (Annotated)
• Understanding Open Source Software - by Red Hat's Mark Webbink, Esq.
• Understanding Open Source and Free Software Licensing - O'Reilly Media - Written by St. Laurent who is an experienced lawyer with a long-time interest in intellectual property, particularly software licensing. This book helps you make sense of the different options available to you. This concise guide focuses on annotated licenses, offering an in-depth explanation of how they compare and interoperate, and how license choices affect project possibilities. Written in clear language that you don't have to be a lawyer to understand, the book answers such questions as: What rights am I giving up? How will my use of OS/FS licensing affect future users or future developers? Does a particular use of this software--such as combining it with proprietary software--leave me vulnerable to lawsuits?