A working reference for the vocabulary of transportation — organized by mode and domain. Definitions cover infrastructure, operations, policy, and emerging mobility, written for industry professionals, planners, journalists, and analysts. Fundamentals Mode A specific form of transportation defined by the infrastructure and vehicle type it uses — road, rail, air, water, pipeline. Modal choice involves trade-offs between speed, cost, capacity, and environmental impact. Modal shift — moving freight or passengers from one mode to another — is a primary lever of transportation policy.