PHP许可证是指授权PHP编程语言及其引擎的许可证。PHP编程语言使用的许可证是在BSD许可证基础上进行的修改。PHP许可证是一种开放源代码许可证，这意味着它允许使用和修改源代码，并在修改后的软件中重新发布代码。让我们看看PHP许可证的一些主要方面。

PHP许可证允许用户在各种条件下使用软件，只要遵守许可证上所列的条件即可。一些最常见的条件是将许可证书保留在软件之中，附加到软件的所有副本中和在任何修改后的软件中包含软件作者的名字和联系信息。

PHP许可证原文：
Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
3. The name "PHP" must not be used to endorse or promote products derived from this software without prior written permission. For written permission, please contact group@php.net.
4. Products derived from this software may not be called "PHP", nor may "PHP" appear in their name, without prior written permission from group@php.net. You may indicate that your software works in conjunction with PHP by saying "Foo for PHP" instead of calling it "PHP Foo" or "phpfoo"
5. The PHP Group may publish revised and/or new versions of the license from time to time. Each version will be given a distinguishing version number.

许可证还要求用户不得使用“PHP”作为产品或衍生品的名称，除非获得了PHP Group的书面许可。这意味着，如果您编写一个用PHP编写的网站管理系统，您应该避免使用“PHP”作为您的软件名称，或者您的软件名称不能包含“PHP”。

另外，作者需要保留许可证，同时还需要遵守其他的规定，例如，在任何修改后的版本中包含原软件作者的名字和联系信息，不得隐瞒作者以及原软件的主要贡献者。

PHP许可证原文：
4. Products derived from this software may not be called "PHP", nor may "PHP" appear in their name, without prior written permission from group@php.net. You may indicate that your software works in conjunction with PHP by saying "Foo for PHP" instead of calling it "PHP Foo" or "phpfoo"

PHP许可证头文件还包含了一些其他有用的声明。例如，这个声明表示，许可证对PHP语言不包含任何的保证：

PHP许可证原文：
THIS SOFTWARE IS PROVIDED BY THE PHP DEVELOPMENT TEAM "AS IS" AND ANY EXPRESSED 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 PHP DEVELOPMENT TEAM OR ITS 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, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

显然，在使用PHP编写软件时，用户需要了解并遵守PHP许可证的所有规定。这将确保您的软件经过授权和合法，将不会引发版权问题。幸运的是，PHP许可证非常明确，它非常简单明了地说明了许可证使用的条件和限制。

总之，PHP许可证是一种灵活的授权模式，使许多用户能够使用和修改PHP编程语言的源代码。随着时间的推移，PHP许可证可能会发生变化，因此，当您使用PHP编写软件时，应该了解和遵守当前的许可证条件和规定，这可以让你的软件合法并避免版权问题。