What is the difference between MWD and LWD?

MWD stands for Measurement While Drilling.

LWD stands for Logging While Drilling. 

Data acquired:
MWD:
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1. Log acquired:
Gamma Ray (GR) - tells lithology encountered as a well is drilled.
Resistivity (RES) - tells fluid encountered as a well is drilled. Differentiate between water or hydrocarbon.

2. Directional survey

Those data needed from beginning of drilling to make sure the well is heading in the right direction and right mud weight is applied. 

LWD:
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Log acquired:
Gamma Ray (GR)
Resistivity (RES)
Neutron-Density (NEU-DEN) - differentiate between water, oil and gas phase.
Caliper (CALI) - gives continuous measurement of the size and shape of a borehole along its depth and is commonly used in hydrocarbon exploration when drilling wells. The measurements that are recorded can be an important indicator of cave ins or shale swelling in the borehole, which can affect the results of other well logs. (source wikipedia).

Data from LWD is needed when the well enters the objective section (target section expected to contain hyrdrocarbon).

LWD cost more than MWD+logging using wireline. 
Today I learnt that:
1. During exploration campaign, conventional practice prefers MWD+Wireline logging than LWD. Though MWD could not differentiate between oil and gas phase, that can be assessed via oil/gas shows in cuttings. Wireline logging will ascertain the exact depth of lithology and each fluid. 

2. There are teams' experience drilling Basement rock didnt get good LWD data - due to high vibration during low ROP (rate of penetration). When on LWD mode, well drilling needs to slow down to record the data. 

Disclaimer:
The sharing is based on my personal interpretation and understanding. It does not represent any company or engineering body/technical journal.