Question: While developing more and more customized Wordpress themes, I began adding more custom functions to my theme's functions.php file. While I try to make their names to be self-explanatory, I think this is not enough.

Considering that you might not be the only web developer working on a theme, or that there might be somebody else who will be put in charge of continuing the development of said theme, I wonder, how should we name our functions to distinguish them from core WP ones?

Edit: Re-worded the question
**Q: Are there any patterns that help developers co-working on the projects namespace functions to avoid confusion whether they are native to Wordpress or not?**

Answer: 
I almost used the same convention as @GhostToas but to me I usually use classes to minimize conflict.
For internal or company project: `class MyCompany_Classname {}`
For Client specific project: `class ClientProject_Classname {}`
Using a class will absolutely help you avoid conflicts and thus, you can name your function using generic function names. Say for example:

```
class MyCompany_ThemeSettings {
    function saveSettings() {
    }

    function displaySettings() {
    }

    function getSettings() {
    }
}

```
As I work for a company, I typically prepend my function names with our company nickname, for functions that tend to stick around. Example: `mycompany_custom_excerpt()`. 

For project-specific functions, I tend to use a nickname that represents the project (such as the theme's name). Example: `client_related_physicians_check()`.

Or you could just as easily use your unique handle if you are a freelancer. For example: `ghosttoast_hide_admin_user()`.

Where those prefixes may be found in many functions. But if you are creating so many functions to live in `functions.php` that you are getting confused, perhaps you should consider including an external file. Example: `mycompany_functions.php`. 

Or consider developing actual plugins that you can reuse across future products: `mycompany-custom-excerpt.php`.