Flask is licensed under a three clause BSD License. It basically means: do whatever you want with it as long as the copyright in Flask sticks around, the conditions are not modified and the disclaimer is present. Furthermore you must not use the names of the authors to promote derivatives of the software without written consent.
The full license text can be found below (Flask License). For the documentation and artwork different licenses apply.
The following section contains the full license texts for Flask and the documentation.
Copyright (c) 2014 by Armin Ronacher and contributors. See AUTHORS for more details.
Some rights reserved.
Redistribution and use in source and binary forms of the software as well as documentation, with or without modification, are permitted provided that the following conditions are met:
THIS SOFTWARE AND DOCUMENTATION IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS “AS IS” AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE AND DOCUMENTATION, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
Copyright (c) 2010 by Armin Ronacher.
Some rights reserved.
This logo or a modified version may be used by anyone to refer to the Flask project, but does not indicate endorsement by the project.
Redistribution and use in source (the SVG file) and binary forms (rendered PNG files etc.) of the image, with or without modification, are permitted provided that the following conditions are met:
Note: we would appreciate that you make the image a link to http://flask.pocoo.org/ if you use it on a web page.