What is this virtual memory for the applications on macOs?
About Virtual Memory
Virtual memory allows an operating system to escape the limitations of physical RAM. The virtual memory manager creates a logical address space (or “virtual” address space) for each process and divides it up into uniformly-sized chunks of memory called pages. The processor and its memory management unit (MMU) maintain a page table to map pages in the program’s logical address space to hardware addresses in the computer’s RAM. When a program’s code accesses an address in memory, the MMU uses the page table to translate the specified logical address into the actual hardware memory address. This translation occurs automatically and is transparent to the running application.
From Apple Developer Documentation

What is secure virtual memory on Mac?
To keep your information safe, macOS uses secure virtual memory. Virtual memory is a technique computers use to temporarily move data from random-access memory (RAM) to the hard disk if the amount of available RAM is limited. If the data written to the hard disk as virtual memory is unencrypted, and is never overwritten, it could be captured if the hard disk is scanned, creating a potential security risk.
Secure virtual memory in macOS eliminates this risk by encrypting the data in virtual memory. Secure virtual memory is always on, so data is kept secure while it’s swapped between your hard disk and RAM. The RAM on your Mac contains no information when it’s turned off.
From Apple Support