What is the meaning of individual Resource Manager like Heap, Btree, XLOG etc from WAL file?

Question

In PostgreSQL v15 I have installed pg_walinspect extension. I am trying to understand what is individual resource manager fields.

Like I understand resource manager tells us where individual data change has happened. I did several actions like INSERT, UPDATE, CREATE TABLE, CHECKPOINT and got result (I have heavily clean the output, just to display one resource manager type per row):

 start_lsn  |   end_lsn   |  xid   | resource_manager | record_type       |
------------+-------------+--------+------------------+-------------------+
15/61E54B08 | 15/61E54B48 | 337813 | Heap             | INSERT            |
15/61E54B48 | 15/61E54C10 | 337813 | Btree            | INSERT_LEAF       |
15/61E577A8 | 15/61E57820 |      0 | XLOG             | CHECKPOINT_ONLINE |
15/61E61C78 | 15/61E61CA8 | 337848 | Standby          | LOCK              |
15/61E61CA8 | 15/61E61CD8 | 337848 | Storage          | CREATE            |
15/61E75758 | 15/61E75A98 | 337848 | Heap2            | MULTI_INSERT      |
15/61E83610 | 15/61E838B8 | 337848 | Transaction      | COMMIT            |

Now look at resource_manager attribute. What is the meaning of:

• Heap - Is this memory or disk? It looks to me it is memory.
• Btree - I assume index related (b-tree index).
• XLOG - I assume WAL log related (I executed CHECKPOINT command).
• Standby - No idea on this one.
• Storage - I assume related to disk storage.
• Heap2 - Probably similar to Heap, but what?
• Transaction - Happens on commit/rollback.