That is one of thedescriptive definitions of a liquid.
The measurement of how closely particles are packed together is usually by state of matter. Gasses are measured as have particles that are further apart than liquids or solids for example.
Closely packed ,tightly packed
The phase when the particles are most closely packed together is the solid form. liquid is farther apart, and gases are even farther.
A particle that is closely packed together would typically be in a solid state. In a solid, particles are arranged in a highly organized structure, with little room for movement. This close packing of particles gives solids their characteristic shape and volume.
I think that what you mean to ask is, are the particles in a solid packed close together, which they are, particularly in comparison to a gas, in which the particles are rather distant from each other. However, you can pack solid particles in various ways, closely or distantly. The solidity of the particle does not dictate the type of packing.
Atoms are in a solid but as in particles it depends on the object.
In a solid, particles are indeed closely packed together, but they are not completely motionless. The particles still have vibrational motion around their fixed positions. This vibrational motion increases with temperature, causing the solid to expand as the particles move more vigorously.
In a solid state, particles move the slowest and are closely packed together. This results in a fixed shape and volume for solids.
solid.
solid
Air particles are most closely packed together near the Earth's surface, where atmospheric pressure is highest. As you move higher up in the atmosphere, air particles become more spread out due to decreasing pressure.
Protons and neutrons consist of three confined quarks each.