Purpose: This manuscript synthesizes and integrates a series of previously published innovative sonographic concepts into a unified framework of Functional Lung Ultrasound (FLUS), introducing lung ultrasound as a real-time bedside functional “visual spirometry” tool. Rather than focusing on artefact-based interpretation, it reframes pulmonary sonography as a structural–functional imaging modality. The primary aim is to systematize the diagnostic meaning of novel sonographic entities—namely the Twinkling White Area (TWA), Bat Sign dynamics, vascular echo patterns, and pleural separation—with particular emphasis on lung ultrasound’s role in the bedside functional diagnosis, phenotyping, and monitoring of obstructive lung syndromes, within a coherent physiological and pathophysiological model of peripheral lung function. Methods: This work is based on a structured reinterpretation of serial ultrasound examinations previously performed in healthy subjects and in over 600 patients with obstructive, interstitial, infectious, malignant, and vascular lung diseases, as reported across separate original publications. Sonographic features of the Merlin Space—including pleural line behavior, rib-shadow geometry, TWA morphology, and respiratory excursion—are collectively reanalyzed and integrated with their corresponding CT correlations, morphologic substrates, and hemodynamic implications in order to construct a reproducible structure–function continuum. Results: The TWA is consolidated as a genuine subpleural reflective interface dynamically linked to peripheral lung density, representing the baseline architectural unit of the aerated lung. The Bat Sign is redefined as a functional continuum rather than a static landmark: the Healthy Bat preserves symmetric TWA geometry, rib-shadow distance, and respiratory motion, whereas the Sick Bat exhibits deformation, asymmetry, and altered dynamics reflecting early parenchymal or obstructive involvement. The Front Sight in Rear Sight sign is confirmed as a dual-vascular echo configuration corresponding to pulmonary infarction supported by bronchial collateral perfusion. Posterior basal pleural separation emerges as a functional marker of chronic, non-exudative, viscerally confined pleural–subpleural remodeling rather than acute inflammatory pleural disease. Conclusion: This integrated framework formally establishes Functional Lung Ultrasound (FLUS) as a real-time, bedside “visual spirometry” modality, in which echo morphology, motion analysis, and perfusion patterns translate directly into functional assessment of airflow, density distribution, and peripheral vascular dynamics. By unifying structural and physiological echo phenomena, FLUS positions lung ultrasound as a true functional imaging tool for obstructive, interstitial, infectious, malignant, and vascular lung syndromes.