Here are the data structures with brief descriptions:

biosParmBlock	BIOS parameter block
cache_t	Cache for an SD data block
CID
csd_t
CSDV1
CSDV2
directoryEntry	FAT short directory entry
Extruder	Data to drive one extruder
fat32_boot	Boot sector for a FAT32 volume
fat32_fsinfo	FSINFO sector for a FAT32 volume
fat32BootSector	Boot sector for a FAT16 or FAT32 volume
fat_boot	Boot sector for a FAT12/FAT16 volume
fpos_t	Internal type for istream do not use in user apps
GCode
masterBootRecord	Master Boot Record
partitionTable	MBR partition table entry
PrinterState
PrintLine
RFHardwareSerial
ring_buffer
Sd2Card	Raw access to SD and SDHC flash memory cards
SdBaseFile	Base class for SdFile with Print and C++ streams
SdFat	Integration class for the SdFat library
SdFile	SdBaseFile with Print
SdVolume	Access FAT16 and FAT32 volumes on SD and SDHC cards
SerialOutput
TemperatureController
UIDisplay
UIMenu
UIMenuEntry