Chakra Reserve
Your normal chakra reserve is the amount shown by /chakra info. It starts at 100 maximum chakra for a new shinobi and is spent whenever an activity or jutsu lists a chakra cost.
Reserve Seal
The Reserve Seal is an item you can craft in the workshop. While you own it, meditation can store chakra in the seal, up to 30 points. Stored chakra does not increase your normal maximum; it is an emergency reserve you can release later from the chakra information flow.
Crafting one currently costs 1 Blank Scroll + 4 Chakra Residue. If you dismantle it, the recovery recipe returns 1 Blank Scroll + 2 Chakra Residue, so dismantling is not a full refund.
Use the seal when you expect a long farming or combat session. Filling it during meditation gives you a buffer without changing your normal regeneration rules.