What is a SQL Server "lop"?
A LOP is a "Logged Operation" they have identifiers and contexts internally.

  LOP  LopDesc (Operation), LopCtxt (LOP Context)
    1,     LOP_FORMAT_PAGE,        LCX_TEXT_MIX
    1,     LOP_FORMAT_PAGE,       LCX_CLUSTERED
    1,     LOP_FORMAT_PAGE,      LCX_INDEX_LEAF
    1,     LOP_FORMAT_PAGE,  LCX_INDEX_INTERIOR
    2,     LOP_INSERT_ROWS,        LCX_TEXT_MIX
    2,     LOP_INSERT_ROWS,       LCX_CLUSTERED
    2,     LOP_INSERT_ROWS,      LCX_INDEX_LEAF
    2,     LOP_INSERT_ROWS,  LCX_INDEX_INTERIOR
    3,     LOP_DELETE_ROWS,   LCX_MARK_AS_GHOST
    3,     LOP_DELETE_ROWS,  LCX_INDEX_INTERIOR
    4,      LOP_MODIFY_ROW,             LCX_IAM
    4,      LOP_MODIFY_ROW,             LCX_PFS
    4,      LOP_MODIFY_ROW,            LCX_HEAP
    4,      LOP_MODIFY_ROW,        LCX_TEXT_MIX
    4,      LOP_MODIFY_ROW,       LCX_BOOT_PAGE
    4,      LOP_MODIFY_ROW,       LCX_CLUSTERED
    4,      LOP_MODIFY_ROW,       LCX_OBJECT_ID
    5,   LOP_MODIFY_HEADER,            LCX_HEAP
    5,   LOP_MODIFY_HEADER,      LCX_INDEX_LEAF
    6,  LOP_MODIFY_COLUMNS,       LCX_CLUSTERED
    7,        LOP_SET_BITS,             LCX_PFS
    7,        LOP_SET_BITS,            LCX_SGAM
   10,  LOP_SET_FREE_SPACE,             LCX_PFS
   11,    LOP_DELETE_SPLIT,       LCX_CLUSTERED
   11,    LOP_DELETE_SPLIT,      LCX_INDEX_LEAF
   13,    LOP_EXPUNGE_ROWS,       LCX_CLUSTERED
   16, LOP_FILE_HDR_MODIFY,     LCX_FILE_HEADER
   18,     LOP_COUNT_DELTA,       LCX_CLUSTERED
   19,     LOP_ROOT_CHANGE,       LCX_CLUSTERED
   22,       LOP_INSYSXACT,       LCX_CLUSTERED
   22,       LOP_INSYSXACT,      LCX_INDEX_LEAF
   22,       LOP_INSYSXACT,  LCX_INDEX_INTERIOR
  128,      LOP_BEGIN_XACT,            LCX_NULL
  129,     LOP_COMMIT_XACT,            LCX_NULL
  131,       LOP_PREP_XACT,            LCX_NULL
  137,        LOP_HOBT_DDL,            LCX_NULL
  140,      LOP_HOBT_DELTA,            LCX_NULL
  141,       LOP_LOCK_XACT,            LCX_NULL
  148,        LOP_BP_DBVER,            LCX_NULL
  150,      LOP_BEGIN_CKPT,            LCX_NULL
  152,       LOP_XACT_CKPT,  LCX_BOOT_PAGE_CKPT
  153,        LOP_END_CKPT,            LCX_NULL
  211,     LOP_SHRINK_NOOP,            LCX_NULL


It looks like the LopCtxt is a kind of breakdown of the logged operation into atoms.

@sp_BlitzErik provided this blog post find which adds a lot detail.