Holgado vs. suelto vs. flojo

The Spanish words 'holgado', 'suelto', and 'flojo' all generally mean ‘loose’ or ‘loose-fitting’ in the context of clothes or shoes. However, these words are used in slightly different contexts and have slightly different connotations.

Holgado

Holgado refers to clothing or footwear that is loose fitting in a comfortable or accommodating manner. It implies a positive degree of roominess, making it perfect for describing relaxed-fit clothing.
Esta camisa es muy holgada.
(This shirt is very loose fitting.)
Me gustan los zapatos holgados porque son más cómodos.
(I like roomy shoes because they are more comfortable.)

Suelto

Suelto often refers to something that is unattached or free. In terms of clothes, it means loose in the sense of being unbound or not form-fitting.
El botón de mi camisa está suelto.
(The button on my shirt is loose.)
Los pantalones sueltos son populares este año.
(Loose pants are popular this year.)

Flojo

'Flojo' essentially means weak, lacking tension or slack. When referring to clothing, 'flojo' indicates not just looseness but a lack of proper fit that can imply a garment is too large or hasn't been adjusted correctly.
Este cinturón está muy flojo y no sostiene mis pantalones.
(This belt is too slack and doesn't hold my pants.)
Me puse una camisa demasiado floja y tener que ajustarla siempre es incómodo.
(I wore a shirt that was too slack and always having to adjust it is uncomfortable.)

Summary

'Holgado', 'suelto', and 'flojo' each describe different facets of looseness when referring to clothes or shoes. ‘Holgado’ implies comfort and spaciousness. 'Suelto' often involves a sense of being unbound. While 'flojo' refers to lack of tension or fit.