wrt (openwrt / lede) initramfs

Do you know what initramfs-kernel mean? I know

-factory/squashfs-sysupgrade

. How can I do it or what is it? which is better? I just don't understand what the initramfs-kernel mean. I have

1900ACS v2

and

-Link DL-860l B1

, but I only use

-factory

and

-sysupgrade

. What does the

-kernel

mean? When would I use those? I would even fear to install that. So, continuing, like

-17.01.2-ramips-mt7621-dir-860l-b1-initramfs-kernel.bin

, what does this mean? can i use it and if so, what is the difference between

-17.01.2-ramips-mt7621-dir-860l-b1-squashfs-factory.bin

(which I know what it does and how) or

-17.01.2-ramips-mt7621-dir-860l-b1-squashfs-sysupgrade.bin

(which I know what it does and how).