What is the order of final measurement result digit using qiskit with IBMQ?

When I run the circuit on the real device, the result will return a series of digits. Do they represent the virtual qubits (logical qubits) or physical qubits? What is the order of the bit strings?

Please read this intro chapter from qiskit-textbook:
qiskit.org/textbook/ch-states/atoms-computation.html

So far, the readout from most could-access hardware directly use physical qubits (you can also view it as using one physical qubit to encode a logical qubit). The order of the bit strings depends on the platform. In Qiskit, start reading the binary string from the last qubit . This is because people want to know the largest binary base first (explained in qiskit-textbook). For example,

$$9213=(1\times 2^{13})+(0\times 2^{12})+\cdots$$

This means we will start reading the measurement result from the 14th qubit and have $9213\to 10001111111101$. Things will be reversed in other platforms like Cirq and PaddleQuantum.