Four names have been given, out of which three are alike in some manner and one is different. Select the odd one.

Let's analyze all the options:

(a) Rajdhani Express → A premium long-distance train known for high speed and priority.
(b) Milan Rath Express → No well-known train by this name (Possible incorrect option).
(c) Shatabdi Express → A daytime, high-speed intercity train known for shorter journeys.
(d) Garib Rath Express → A budget-friendly long-distance train with fully AC coaches.
Odd One:
Rajdhani, Shatabdi, and Garib Rath are all well-known categories of Indian trains. 
Milan Rath Express does not belong to any specific well-known category and seems different. 
Thus, the correct option is (b) Milan Rath Express.