The reciprocal terms of the GPL are very elegant. They say that the creator of the software is granting you various rights and freedoms, with the understanding that you will provide those who receive your software those same rights and freedoms.

The simplest way to comply with these term is to make your software available under the GPL license as well. But you do not have to so, as long as the freedoms of the GPL are provided by your license.

There is often confusion about reciprocal terms when it comes to who the source code must be made available to. If you embed or extend FOSS that has a reciprocal license you are typically required to make your source code (and any changes made to the FOSS components) available to the people that you distribute your product or software to. You do not have to make your changes available to the world - you do not have to make your source code available on the internet. However in the case of the GPL, the people receiving your product (with source code) are usually granted the right to distribute that source code to whoever they want - so they are at liberty to make the source code publicly available. If you do not distribute your software, for example if it is only used internally within an organization, you do not have to make your source code available externally.

The “reciprocal” nature of the license is, if I understand you correctly, the same as its “copyleft” nature. That is, a recipient of the work gains benefit from the freedoms in the work, but if they choose to themselves redistribute the work, they may only do so on condition that they reciprocate by granting the same freedoms to each recipient.