Terms to know

JCL
Job Control Language
TPS
Transactions per second
CHPID
Channel path identifiers
PCHID
Physical channel identifiers
DASD
Direct access storage device
WLM
Workload management
TSO
Time Sharing Option/Extensions
ISPF
Interactive System Productivity Facility
CLIST
Command list
PA (PA1,PA3) keys
Program Action keys
VSAM
Virtual Storage Access Manager
VSM
Virtual Storage Manager
KSDS
Key sequenced data set
QSAM
Queued Sequential Access Method
BSAM
Basic Sequential Access Method
BDAM
Basic Direct Access Method
BPAM
Basic Partitioned Access Method
VSAM
Virtual Storage Access Method
DASD
Direct Access Storage Device, another name for a disk drive.
HDA
Head Disk Assembly (disk drive)
CKD
Count Key Data (data record format)
ECKD
Extended Count Key Data (current data record format)
VTOC
Volume Table of Contents
HLQ
High-level qualifier, first name used in a dataset name.
LLQ
Lowest-level qualifier, last name used in dataset name.
CICS
Customer Interaction Control System